What is the use of bind() in JavaScript?
Bind creates a new function that will force the this inside the function to be the parameter passed to bind().
Here's an example that shows how to use bind to pass a member method around that has the correct this:
var myButton = {
content: 'OK',
click() {
console.log(this.content + ' clicked');
}
};
myButton.click();
var looseClick = myButton.click;
looseClick(); // not bound, 'this' is not myButton - it is the globalThis
var boundClick = myButton.click.bind(myButton);
boundClick(); // bound, 'this' is myButton
Which prints out:
OK clicked
undefined clicked
OK clicked
You can also add extra parameters after the 1st (this) parameter and bind will pass in those values to the original function. Any additional parameters you later pass to the bound function will be passed in after the bound parameters:
// Example showing binding some parameters
var sum = function(a, b) {
return a + b;
};
var add5 = sum.bind(null, 5);
console.log(add5(10));
Which prints out:
15
Check out JavaScript Function bind for more info and interactive examples.
Update: ECMAScript 2015 adds support for => functions. => functions are more compact and do not change the this pointer from their defining scope, so you may not need to use bind() as often. For example, if you wanted a function on Button from the first example to hook up the click callback to a DOM event, the following are all valid ways of doing that:
var myButton = {
... // As above
hookEvent(element) {
// Use bind() to ensure 'this' is the 'this' inside click()
element.addEventListener('click', this.click.bind(this));
}
};
Or:
var myButton = {
... // As above
hookEvent(element) {
// Use a new variable for 'this' since 'this' inside the function
// will not be the 'this' inside hookEvent()
var me = this;
element.addEventListener('click', function() { me.click() });
}
};
Or:
var myButton = {
... // As above
hookEvent(element) {
// => functions do not change 'this', so you can use it directly
element.addEventListener('click', () => this.click());
}
};
The simplest use of bind() is to make a function that, no matter
how it is called, is called with a particular this value.
x = 9;
var module = {
x: 81,
getX: function () {
return this.x;
}
};
module.getX(); // 81
var getX = module.getX;
getX(); // 9, because in this case, "this" refers to the global object
// create a new function with 'this' bound to module
var boundGetX = getX.bind(module);
boundGetX(); // 81
Please refer to this link on MDN Web Docs for more information:
Function.prototype.bind()
bind allows-
set the value of "this" to an specific object. This becomes very helpful as sometimes this is not what is intended.
reuse methods
curry a function
For example, you have a function to deduct monthly club fees
function getMonthlyFee(fee){
var remaining = this.total - fee;
this.total = remaining;
return this.name +' remaining balance:'+remaining;
}
Now you want to reuse this function for a different club member. Note that the monthly fee will vary from member to member.
Let's imagine Rachel has a balance of 500, and a monthly membership fee of 90.
var rachel = {name:'Rachel Green', total:500};
Now, create a function that can be used again and again to deduct the fee from her account every month
//bind
var getRachelFee = getMonthlyFee.bind(rachel, 90);
//deduct
getRachelFee();//Rachel Green remaining balance:410
getRachelFee();//Rachel Green remaining balance:320
Now, the same getMonthlyFee function could be used for another member with a different membership fee. For Example, Ross Geller has a 250 balance and a monthly fee of 25
var ross = {name:'Ross Geller', total:250};
//bind
var getRossFee = getMonthlyFee.bind(ross, 25);
//deduct
getRossFee(); //Ross Geller remaining balance:225
getRossFee(); //Ross Geller remaining balance:200
From the MDN docs on Function.prototype.bind() :
The bind() method creates a new function that, when called, has its
this keyword set to the provided value, with a given sequence of
arguments preceding any provided when the new function is called.
So, what does that mean?!
Well, let's take a function that looks like this :
var logProp = function(prop) {
console.log(this[prop]);
};
Now, let's take an object that looks like this :
var Obj = {
x : 5,
y : 10
};
We can bind our function to our object like this :
Obj.log = logProp.bind(Obj);
Now, we can run Obj.log anywhere in our code :
Obj.log('x'); // Output : 5
Obj.log('y'); // Output : 10
This works, because we bound the value of this to our object Obj.
Where it really gets interesting, is when you not only bind a value for this, but also for its argument prop :
Obj.logX = logProp.bind(Obj, 'x');
Obj.logY = logProp.bind(Obj, 'y');
We can now do this :
Obj.logX(); // Output : 5
Obj.logY(); // Output : 10
Unlike with Obj.log, we do not have to pass x or y, because we passed those values when we did our binding.
Variables has local and global scopes. Let's suppose that we have two variables with the same name. One is globally defined and the other is defined inside a function closure and we want to get the variable value which is inside the function closure. In that case we use this bind() method. Please see the simple example below:
var x = 9; // this refers to global "window" object here in the browser
var person = {
x: 81,
getX: function() {
return this.x;
}
};
var y = person.getX; // It will return 9, because it will call global value of x(var x=9).
var x2 = y.bind(person); // It will return 81, because it will call local value of x, which is defined in the object called person(x=81).
document.getElementById("demo1").innerHTML = y();
document.getElementById("demo2").innerHTML = x2();
<p id="demo1">0</p>
<p id="demo2">0</p>
Summary:
The bind() method takes an object as an first argument and creates a new function. When the function is invoked the value of this in the function body will be the object which was passed in as an argument in the bind() function.
How does this work in JS anyway
The value of this in javascript is dependent always depends on what Object the function is called. The value of this always refers to the object left of the dot from where is the function is called. In case of the global scope this is window (or global in nodeJS). Only call, apply and bind can alter the this binding differently. Here is an example to show how the this keyword works:
let obj = {
prop1: 1,
func: function () { console.log(this); }
}
obj.func(); // obj left of the dot so this refers to obj
const customFunc = obj.func; // we store the function in the customFunc obj
customFunc(); // now the object left of the dot is window,
// customFunc() is shorthand for window.customFunc()
// Therefore window will be logged
How is bind used?
Bind can help in overcoming difficulties with the this keyword by having a fixed object where this will refer to. For example:
var name = 'globalName';
const obj = {
name: 'myName',
sayName: function () { console.log(this.name);}
}
const say = obj.sayName; // we are merely storing the function the value of this isn't magically transferred
say(); // now because this function is executed in global scope this will refer to the global var
const boundSay = obj.sayName.bind(obj); // now the value of this is bound to the obj object
boundSay(); // Now this will refer to the name in the obj object: 'myName'
Once the function is bound to a particular this value we can pass it around and even put it on properties on other objects. The value of this will remain the same.
The bind() method creates a new function instance whose this value is bound to the value that was passed into bind().
For example:
window.color = "red";
var o = { color: "blue" };
function sayColor(){
alert(this.color);
}
var objectSayColor = sayColor.bind(o);
objectSayColor(); //blue
Here, a new function called objectSayColor() is created from sayColor() by calling bind() and passing in the object o. The objectSayColor() function has a this value equivalent to o, so calling the function, even as a global call, results in the string “blue” being displayed.
Reference : Nicholas C. Zakas - PROFESSIONAL JAVASCRIPT® FOR WEB DEVELOPERS
I will explain bind theoretically as well as practically
bind in javascript is a method -- Function.prototype.bind . bind is a method. It is called on function prototype. This method creates a function whose body is similar to the function on which it is called but the 'this' refers to the first parameter passed to the bind method. Its syntax is
var bindedFunc = Func.bind(thisObj,optionsArg1,optionalArg2,optionalArg3,...);
Example:--
var checkRange = function(value){
if(typeof value !== "number"){
return false;
}
else {
return value >= this.minimum && value <= this.maximum;
}
}
var range = {minimum:10,maximum:20};
var boundedFunc = checkRange.bind(range); //bounded Function. this refers to range
var result = boundedFunc(15); //passing value
console.log(result) // will give true;
Creating a new Function by Binding Arguments to Values
The bind method creates a new function from another function with one or more arguments bound to specific values, including the implicit this argument.
Partial Application
This is an example of partial application. Normally we supply a function with all of its arguments which yields a value. This is known as function application. We are applying the function to its arguments.
A Higher Order Function (HOF)
Partial application is an example of a higher order function (HOF) because it yields a new function with a fewer number of argument.
Binding Multiple Arguments
You can use bind to transform functions with multiple arguments into new functions.
function multiply(x, y) {
return x * y;
}
let multiplyBy10 = multiply.bind(null, 10);
console.log(multiplyBy10(5));
Converting from Instance Method to Static Function
In the most common use case, when called with one argument the bind method will create a new function that has the this value bound to a specific value. In effect this transforms an instance method to a static method.
function Multiplier(factor) {
this.factor = factor;
}
Multiplier.prototype.multiply = function(x) {
return this.factor * x;
}
function ApplyFunction(func, value) {
return func(value);
}
var mul = new Multiplier(5);
// Produces garbage (NaN) because multiplying "undefined" by 10
console.log(ApplyFunction(mul.multiply, 10));
// Produces expected result: 50
console.log(ApplyFunction(mul.multiply.bind(mul), 10));
Implementing a Stateful CallBack
The following example shows how using binding of this can enable an object method to act as a callback that can easily update the state of an object.
function ButtonPressedLogger()
{
this.count = 0;
this.onPressed = function() {
this.count++;
console.log("pressed a button " + this.count + " times");
}
for (let d of document.getElementsByTagName("button"))
d.onclick = this.onPressed.bind(this);
}
new ButtonPressedLogger();
<button>press me</button>
<button>no press me</button>
As mentioned, Function.bind() lets you specify the context that the function will execute in (that is, it lets you pass in what object the this keyword will resolve to in the body of the function.
A couple of analogous toolkit API methods that perform a similar service:
jQuery.proxy()
Dojo.hitch()
Bind Method
A bind implementation might look something like so:
Function.prototype.bind = function () {
const self = this;
const args = [...arguments];
const context = args.shift();
return function () {
return self.apply(context, args.concat([...arguments]));
};
};
The bind function can take any number of arguments and return a new function.
The new function will call the original function using the JS Function.prototype.apply method.The apply method will use the first argument passed to the target function as its context (this), and the second array argument of the apply method will be a combination of the rest of the arguments from the target function, concat with the arguments used to call the return function (in that order).
An example can look something like so:
function Fruit(emoji) {
this.emoji = emoji;
}
Fruit.prototype.show = function () {
console.log(this.emoji);
};
const apple = new Fruit('🍎');
const orange = new Fruit('🍊');
apple.show(); // 🍎
orange.show(); // 🍊
const fruit1 = apple.show;
const fruit2 = apple.show.bind();
const fruit3 = apple.show.bind(apple);
const fruit4 = apple.show.bind(orange);
fruit1(); // undefined
fruit2(); // undefined
fruit3(); // 🍎
fruit4(); // 🍊
/**
* Bind is a method inherited from Function.prototype same like call and apply
* It basically helps to bind a function to an object's context during initialisation
*
* */
window.myname = "Jineesh";
var foo = function(){
return this.myname;
};
//IE < 8 has issues with this, supported in ecmascript 5
var obj = {
myname : "John",
fn:foo.bind(window)// binds to window object
};
console.log( obj.fn() ); // Returns Jineesh
Consider the Simple Program listed below,
//we create object user
let User = { name: 'Justin' };
//a Hello Function is created to Alert the object User
function Hello() {
alert(this.name);
}
//since there the value of this is lost we need to bind user to use this keyword
let user = Hello.bind(User);
user();
//we create an instance to refer the this keyword (this.name);
Simple Explanation:
bind() create a new function, a new reference at a function it returns to you.
In parameter after this keyword, you pass in the parameter you want to preconfigure. Actually it does not execute immediately, just prepares for execution.
You can preconfigure as many parameters as you want.
Simple Example to understand bind:
function calculate(operation) {
if (operation === 'ADD') {
alert('The Operation is Addition');
} else if (operation === 'SUBTRACT') {
alert('The Operation is Subtraction');
}
}
addBtn.addEventListener('click', calculate.bind(this, 'ADD'));
subtractBtn.addEventListener('click', calculate.bind(this, 'SUBTRACT'));
The bind function creates a new function with the same function body as the function it is calling .It is called with the this argument .why we use bind fun. : when every time a new instance is created and we have to use first initial instance then we use bind fun.We can't override the bind fun.simply it stores the initial object of the class.
setInterval(this.animate_to.bind(this), 1000/this.difference);
function.prototype.bind() accepts an Object.
It binds the calling function to the passed Object and the returns
the same.
When an object is bound to a function, it means you will be able to
access the values of that object from within the function using
'this' keyword.
It can also be said as,
function.prototype.bind() is used to provide/change the context of a
function.
let powerOfNumber = function(number) {
let product = 1;
for(let i=1; i<= this.power; i++) {
product*=number;
}
return product;
}
let powerOfTwo = powerOfNumber.bind({power:2});
alert(powerOfTwo(2));
let powerOfThree = powerOfNumber.bind({power:3});
alert(powerOfThree(2));
let powerOfFour = powerOfNumber.bind({power:4});
alert(powerOfFour(2));
Let us try to understand this.
let powerOfNumber = function(number) {
let product = 1;
for (let i = 1; i <= this.power; i++) {
product *= number;
}
return product;
}
Here, in this function, this corresponds to the object bound to the function powerOfNumber. Currently we don't have any function that is bound to this function.
Let us create a function powerOfTwo which will find the second power of a number using the above function.
let powerOfTwo = powerOfNumber.bind({power:2});
alert(powerOfTwo(2));
Here the object {power : 2} is passed to powerOfNumber function using bind.
The bind function binds this object to the powerOfNumber() and returns the below function to powerOfTwo. Now, powerOfTwo looks like,
let powerOfNumber = function(number) {
let product = 1;
for(let i=1; i<=2; i++) {
product*=number;
}
return product;
}
Hence, powerOfTwo will find the second power.
Feel free to check this out.
bind() function in Javascript
The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.
An example for the first part
grabbed from react package useSt8
import { useState } from "react"
function st8() {
switch(arguments.length) {
case 0: return this[0]
case 1: return void this[1](arguments[0])
default: throw new Error("Expected 0 or 1 arguments")
}
}
function useSt8(initial) {
// this in st8 will be something like [state, setSatate]
return st8.bind(useState(initial))
}
// usage
function Counter() {
const count = useSt8(0);
return (
<>
Count: {count()}
<button onClick={() => count(0)}>Reset</button>
<button onClick={() => count(prevCount => prevCount + 1)}>inc</button>
</>
);
}
An example for the second part
const add = (a, b) => a+b
someThis = this
// new function with this value equal to someThis
add5 = add.bind(someThis, 5)
add5(10) // 15
// we don't use this in add decelartion so this will work too.
add10 = add.bind(null, 10)
add10(5) // 15
Here's the simplest possible explanation:
Say you have a function
function _loop(n) { console.log("so: " + n) }
obviously you can call it like _loop(69) as usual.
Rewrite like this:
var _loop = function() { console.log("so: " + this.n) }
Notice there are now
no arguments as such
you use "this. " to get to the named arguments
You can now call the function like this:
_loop.bind( {"n": 420} )
That's it.
Most typical use case:
A really typical use is when you need to add an argument to a callback.
Callbacks can't have arguments.
So just "rewrite" the callback as above.
Simple example
function lol(second, third) {
console.log(this.first, second, third);
}
lol(); // undefined, undefined, undefined
lol('1'); // undefined, "1", undefined
lol('1', '2'); // undefined, "1", "2"
lol.call({first: '1'}); // "1", undefined, undefined
lol.call({first: '1'}, '2'); // "1", "2", undefined
lol.call({first: '1'}, '2', '3'); // "1", "2", "3"
lol.apply({first: '1'}); // "1", undefined, undefined
lol.apply({first: '1'}, ['2', '3']); // "1", "2", "3"
const newLol = lol.bind({first: '1'});
newLol(); // "1", undefined, undefined
newLol('2'); // "1", "2", undefined
newLol('2', '3'); // "1", "2", "3"
const newOmg = lol.bind({first: '1'}, '2');
newOmg(); // "1", "2", undefined
newOmg('3'); // "1", "2", "3"
const newWtf = lol.bind({first: '1'}, '2', '3');
newWtf(); // "1", "2", "3"
Another usage is that you can pass binded function as an argument to another function which is operating under another execution context.
var name = "sample";
function sample(){
console.log(this.name);
}
var cb = sample.bind(this);
function somefunction(cb){
//other code
cb();
}
somefunction.call({}, cb);
In addition to what have been said, the bind() method allows an object to borrow a method from another object without making a copy of that method. This is known as function borrowing in JavaScript.
i did not read above code but i learn something in simple so want to share here about bind method after bind method we can use it as any normal method.
<pre> note: do not use arrow function it will show error undefined </pre>
let solarSystem = {
sun: 'red',
moon : 'white',
sunmoon : function(){
let dayNight = this.sun + ' is the sun color and present in day and '+this.moon + ' is the moon color and prenet in night';
return dayNight;
}
}
let work = function(work,sleep){
console.log(this.sunmoon()); // accessing the solatSystem it show error undefine sunmmon untill now because we can't access directly for that we use .bind()
console.log('i work in '+ work +' and sleep in '+sleep);
}
let outPut = work.bind(solarSystem);
outPut('day','night')
bind is a function which is available in java script prototype, as the name suggest bind is used to bind your function call to the context whichever you are dealing with for eg:
var rateOfInterest='4%';
var axisBank=
{
rateOfInterest:'10%',
getRateOfInterest:function()
{
return this.rateOfInterest;
}
}
axisBank.getRateOfInterest() //'10%'
let knowAxisBankInterest=axisBank.getRateOfInterest // when you want to assign the function call to a varaible we use this syntax
knowAxisBankInterest(); // you will get output as '4%' here by default the function is called wrt global context
let knowExactAxisBankInterest=knowAxisBankInterest.bind(axisBank); //so here we need bind function call to its local context
knowExactAxisBankInterest() // '10%'
I'm trying to test if an element is visible using protractor. Here's what the element looks like:
<i class="icon-spinner icon-spin ng-hide" ng-show="saving"></i>
When in the chrome console, I can use this jQuery selector to test if the element is visible:
$('[ng-show=saving].icon-spin')
[
<i class="icon-spinner icon-spin ng-hide" ng-show="saving"></i>
]
> $('[ng-show=saving].icon-spin:visible')
[]
However, when I try to do the same in protractor, I get this error at runtime:
InvalidElementStateError:
invalid element state: Failed to execute 'querySelectorAll' on 'Document':
'[ng-show=saving].icon-spin:visible' is not a valid selector.
Why is this not valid? How can I check for visibility using protractor?
This should do it:
expect($('[ng-show=saving].icon-spin').isDisplayed()).toBe(true);
Remember protractor's $ isn't jQuery and :visible is not yet a part of available CSS selectors + pseudo-selectors
More info at https://stackoverflow.com/a/13388700/511069
The correct way for checking the visibility of an element with Protractor is to call the isDisplayed method. You should be careful though since isDisplayed does not return a boolean, but rather a promise providing the evaluated visibility. I've seen lots of code examples that use this method wrongly and therefore don't evaluate its actual visibility.
Example for getting the visibility of an element:
element(by.className('your-class-name')).isDisplayed().then(function (isVisible) {
if (isVisible) {
// element is visible
} else {
// element is not visible
}
});
However, you don't need this if you are just checking the visibility of the element (as opposed to getting it) because protractor patches Jasmine expect() so it always waits for promises to be resolved. See github.com/angular/jasminewd
So you can just do:
expect(element(by.className('your-class-name')).isDisplayed()).toBeTruthy();
Since you're using AngularJS to control the visibility of that element, you could also check its class attribute for ng-hide like this:
var spinner = element.by.css('i.icon-spin');
expect(spinner.getAttribute('class')).not.toMatch('ng-hide'); // expect element to be visible
I had a similar issue, in that I only wanted return elements that were visible in a page object. I found that I'm able to use the css :not. In the case of this issue, this should do you...
expect($('i.icon-spinner:not(.ng-hide)').isDisplayed()).toBeTruthy();
In the context of a page object, you can get ONLY those elements that are visible in this way as well. Eg. given a page with multiple items, where only some are visible, you can use:
this.visibileIcons = $$('i.icon:not(.ng-hide)');
This will return you all visible i.icons
If there are multiple elements in DOM with same class name. But only one of element is visible.
element.all(by.css('.text-input-input')).filter(function(ele){
return ele.isDisplayed();
}).then(function(filteredElement){
filteredElement[0].click();
});
In this example filter takes a collection of elements and returns a single visible element using isDisplayed().
This answer will be robust enough to work for elements that aren't on the page, therefore failing gracefully (not throwing an exception) if the selector failed to find the element.
const nameSelector = '[data-automation="name-input"]';
const nameInputIsDisplayed = () => {
return $$(nameSelector).count()
.then(count => count !== 0)
}
it('should be displayed', () => {
nameInputIsDisplayed().then(isDisplayed => {
expect(isDisplayed).toBeTruthy()
})
})
To wait for visibility
const EC = protractor.ExpectedConditions;
browser.wait(EC.visibilityOf(element(by.css('.icon-spinner icon-spin ng-hide')))).then(function() {
//do stuff
})
Xpath trick to only find visible elements
element(by.xpath('//i[not(contains(#style,"display:none")) and #class="icon-spinner icon-spin ng-hide"]))
element(by.className('your-class-name'))
.isDisplayed()
.then(function (isVisible) {
if (isVisible) { // element is visible
} else { // element is not visible
}
})
.catch(function(err){
console.error("Element is not found! ", err);
})
Here are the few code snippet which can be used for framework which use Typescript, protractor, jasmine
browser.wait(until.visibilityOf(OversightAutomationOR.lblContentModal), 3000, "Modal text is present");
// Asserting a text
OversightAutomationOR.lblContentModal.getText().then(text => {
this.assertEquals(text.toString().trim(), AdminPanelData.lblContentModal);
});
// Asserting an element
expect(OnboardingFormsOR.masterFormActionCloneBtn.isDisplayed()).to.eventually.equal(true
);
OnboardingFormsOR.customFormActionViewBtn.isDisplayed().then((isDisplayed) => {
expect(isDisplayed).to.equal(true);
});
// Asserting a form
formInfoSection.getText().then((text) => {
const vendorInformationCount = text[0].split("\n");
let found = false;
for (let i = 0; i < vendorInformationCount.length; i++) {
if (vendorInformationCount[i] === customLabel) {
found = true;
};
};
expect(found).to.equal(true);
});
Something to consider
.isDisplayed() assumes the element is present (exists in the DOM)
so if you do
expect($('[ng-show=saving]').isDisplayed()).toBe(true);
but the element is not present, then instead of graceful failed expectation, $('[ng-show=saving]').isDisplayed() will throw an error causing the rest of it block not executed
Solution
If you assume, the element you're checking may not be present for any reason on the page, then go with a safe way below
/**
* element is Present and is Displayed
* #param {ElementFinder} $element Locator of element
* #return {boolean}
*/
let isDisplayed = function ($element) {
return (await $element.isPresent()) && (await $element.isDisplayed())
}
and use
expect(await isDisplayed( $('[ng-show=saving]') )).toBe(true);
waitTillElementIsPresent(locator: Locator): promise.Promise<boolean>
{
const EC = protractor.ExpectedConditions;
return browser.wait(EC.visibilityOf(element(by.id('xyz')), browser.params.explicitWaitTime, 'Element taking too long to appear in the DOM');
}
const isDisplayed = await $('div').isDisplayed().then(null, err => false)
I'm trying out Protractor to e2e test Angular app and haven't figured out how to detect if an element has a specific class or not.
In my case, the test clicks on submit button and now I want to know if form[name="getoffer"] has class .ngDirty. What may be the solutions?
describe('Contact form', function() {
beforeEach(function(){
browser.get('http://localhost:9000');
element(by.linkText('Contact me')).click();
});
it('should fail form validation, all fields pristine', function() {
element(by.css('.form[name="getoffer"] input[type="submit"]')).click();
expect(element(by.name('getoffer'))).toHaveClass('ngDirty'); // <-- This line
});
});
One gotcha you have to look out for with using toMatch(), as in the accepted answer, is partial matches. For instance, let's say you have an element that might have the classes correct and incorrect, and you want to test that it has the class correct. If you were to use expect(element.getAttribute('class')).toMatch('correct'), that will return true even if the element has the incorrect class.
My suggestion:
If you want to only accept exact matches, you can create a helper method for it:
var hasClass = function (element, cls) {
return element.getAttribute('class').then(function (classes) {
return classes.split(' ').indexOf(cls) !== -1;
});
};
You can use it like this (taking advantage of the fact that expect automatically resolves promises in Protractor):
expect(hasClass(element(by.name('getoffer')), 'ngDirty')).toBe(true);
If you're using Protractor with Jasmine, you could use toMatch to match as a regular expression...
expect(element(by.name('getoffer')).getAttribute('class')).toMatch('ngDirty');
Also, note that toContain will match list items, if you need that.
Simplest is:
expect(element.getAttribute('class')).toContain("active");
Based on the answer from Sergey K, you could also add a custom matcher to do this:
(coffeescript)
beforeEach(()->
this.addMatchers({
toHaveClass: (expected)->
#message = ()->
"Expected #{#actual.locator_.value} to have class '#{expected}'"
#actual.getAttribute('class').then((classes)->
classes.split(' ').indexOf(expected) isnt -1
)
})
)
Then you can use it in tests like this:
expect($('div#ugly')).toHaveClass('beautiful')
And you'll get the following error if it doesn't:
Message:
Expected div#ugly to have class beautiful
Stacktrace:
Error: Expected div#ugly to have class 'beautiful'
Have you tried this?
const el = element(by.name('getoffer'));
expect(el.getAttribute('class')).toBe('ngDirty')
or a variation of the above...
I made this matcher, I had to wrap it in a promise and use 2 returns
this.addMatchers({
toHaveClass: function(a) {
return this.actual.getAttribute('class').then(function(cls){
var patt = new RegExp('(^|\\s)' + a + '(\\s|$)');
return patt.test(cls);
});
}
});
in my test i can now do stuf like this:
var myDivs = element.all(by.css('div.myClass'));
expect(myDivs.count()).toBe(3);
// test for class
expect(myDivs.get(0)).not.toHaveClass('active');
this also works when an element has multiple classes or when an element has no class attribute at all.
function checkHasClass (selector, class_name) {
// custom function returns true/false depending if selector has class name
// split classes for selector into a list
return $(selector).getAttribute('class').then(function(classes){
var classes = classes.split(' ');
if (classes.indexOf(class_name) > -1) return true;
return false;
});
}
This is how I do it at least, without the need to use the expect function. This function simply returns true if the class is inside the element and false if not. This also uses promises so you would use it like:
checkHasClass('#your-element', 'your-class').then(function(class_found){
if (class_found) console.log("Your element has that class");
});
Edit: I just realized this is essentially the same as the top answer
Here a Jasmine 1.3.x custom toHaveClass matcher with negation .not support plus wait up to 5 seconds (or whatever you specify).
Find the full custom matcher to be added on your onPrepare block in this gist
Sample usage:
it('test the class finder custom matcher', function() {
// These guys should pass OK given your user input
// element starts with an ng-invalid class:
expect($('#user_name')).toHaveClass('ng-invalid');
expect($('#user_name')).not.toHaveClass('ZZZ');
expect($('#user_name')).toNotHaveClass('ZZZ');
expect($('#user_name')).not.toNotHaveClass('ng-invalid');
// These guys should each fail:
expect($('#user_name')).toHaveClass('ZZZ');
expect($('#user_name')).not.toHaveClass('ng-invalid');
expect($('#user_name')).toNotHaveClass('ng-invalid');
expect($('#user_name')).not.toNotHaveClass('ZZZ');
});
One way to achieve this would be to use xpath and use contains()
Example:
var expectElementToHaveClass = function (className) {
var path = by.xpath("//div[contains(#class,'"+ className +"')]");
expect(element.all(path).count()).to.eventually.be.eq(1);
};
You can use the CSS parser to handle this by checking if an element with the given class exists:
expect(element(by.css('.form[name="getoffer"].ngDirty')).isPresent()).toBe(true);
Essentially, you're solving a few problems:
how to get class. class is an html attribute and thus can be retrieved by this command (await is the recommended way these days)
let class = await element.getAttribute('class')
Once you got the value of a class, you want to assert it
// for exact value
expect(class).toBe("active");
// for partial match
expect(class).toContain("active");
// or
expect(class.includes("active")).toBe(true);
// BUT, keep in mind
expect('male').toContain('male');
expect('female').toContain('male');
// BOTH pass