How to check if expression will have a value after evaluating - angularjs

Question

Let's say I have a following template:
"foo['x'] = '{{ myVar }}';"
Is there an angular way of checking if evaluating this against my current scope will give myVar some value ? I've got an array of such small templates and I only want to include them in the document when values are truthy. I was hoping either $interpolate, $parse or $eval might come in handy here. I know for sure that $interpolate is useless. What about the other two ? Maybe it's at least possible to get the name of the assigned value/expression ?
EDIT
I wasn't specific enough. What I was trying to achieve, was checking in advance if for example template '{{ myVar }}' evaluated against the current scope will return an empty string or value of the scope variable (if it exists). The case was really specific - when traversing an array of short templates I wanted to know if a template will return as an empty string or not, and only include it in my final html if it doesn't.

Answer 1

I'm not sure what are you trying to achieve, but to if you want to check if myVar is truthy in current scope, you can:
{{myVar ? "aw yiss" : "nope"}}
Evaluates to "aw yiss" if myVar is truthy and "nope" otherwise.

Answer 2

I ended up with a modified $interpolate provider but maybe someone knows a shorter solution :
app.provider('customInterpolateProvider', [
function $InterpolateProvider() {
var startSymbol = '{{';
var endSymbol = '}}';
this.startSymbol = function(value){
if (value) {
startSymbol = value;
return this;
} else {
return startSymbol;
}
};
this.endSymbol = function(value){
if (value) {
endSymbol = value;
return this;
} else {
return endSymbol;
}
};
this.$get = ['$parse', '$sce', function($parse, $sce) {
var startSymbolLength = startSymbol.length,
endSymbolLength = endSymbol.length;
function $interpolate(text, mustHaveExpression, trustedContext, allOrNothing) {
allOrNothing = !!allOrNothing;
var startIndex,
endIndex,
index = 0,
expressions = [],
parseFns = [],
textLength = text.length,
exp;
var getValue = function (value) {
return trustedContext ?
$sce.getTrusted(trustedContext, value) :
$sce.valueOf(value);
};
var stringify = function (value) {
if (value == null) {
return '';
}
switch (typeof value) {
case 'string':
break;
case 'number':
value = '' + value;
break;
default:
value = angular.toJson(value);
}
return value;
};
var parseStringifyInterceptor = function(value) {
try {
return stringify(getValue(value));
} catch(err) {
console.err(err.toString());
}
};
while(index < textLength) {
if ( ((startIndex = text.indexOf(startSymbol, index)) !== -1) &&
((endIndex = text.indexOf(endSymbol, startIndex + startSymbolLength)) !== -1) ) {
exp = text.substring(startIndex + startSymbolLength, endIndex);
expressions.push(exp);
parseFns.push($parse(exp, parseStringifyInterceptor));
index = endIndex + endSymbolLength;
} else {
break;
}
}
if (!expressions.length && !text.contains(startSymbol) && !text.contains(endSymbol)) {
expressions.push(text);
}
if (!mustHaveExpression) {
var compute = function(values) {
for(var i = 0, ii = expressions.length; i < ii; i++) {
if (allOrNothing && angular.isUndefined(values[i])) {
return;
}
expressions[i] = values[i];
}
return expressions.join('');
};
return angular.extend(function interpolationFn(context) {
var i = 0;
var ii = expressions.length;
var values = new Array(ii);
try {
if (ii && !parseFns.length) {
return expressions[0];
} else {
for (; i < ii; i++) {
values[i] = parseFns[i](context);
}
return compute(values);
}
} catch(err) {
console.err(err.toString());
}
}, {
exp: text,
expressions: expressions,
$$watchDelegate: function (scope, listener, objectEquality) {
var lastValue;
return scope.$watchGroup(parseFns, function interpolateFnWatcher(values, oldValues) {
var currValue = compute(values);
if (angular.isFunction(listener)) {
listener.call(this, currValue, values !== oldValues ? lastValue : currValue, scope);
}
lastValue = currValue;
}, objectEquality);
}
});
}
}
return $interpolate;
}];
}
]);
Lines below were added because in some cases I have a predefined text in my short template and I always want to render it :
if (!expressions.length && !text.contains(startSymbol) && !text.contains(endSymbol)) {
expressions.push(text);
}
if (ii && !parseFns.length) {
return expressions[0];
} else {