How to find JavaScript variable by its name

<script>
var a ="test";
alert(a);
alert(window["a"]);
alert(eval("a"));
</script>

All JS objects (which variables are) are available within their scope as named properties of their parent object. Where no explicit parent exists, it is implicitly the window object.

i.e.:

var x = 'abc';
alert(window['x']); //displays 'abc'

and for a complex object:

var x = {y:'abc'};
alert(x['y']); //displays 'abc'

and this can be chained:

var x = {y:'abc'};
alert(window['x']['y']); //displays 'abc'

If you are wanting a variable that is declared in the global context, it is attached to the window object. ex: window["variableName"]. All variables are a hash table value within their scope.

If you have to use dotted notation, then you will want to follow kennebec's suggestion, to navigate through the object hierarchy. eval() can work as well, but is a more expensive operation than is probably needed.

If your string references a 'deep' property of a global, like 'Yankee.console.format' you can step through the references:

String.prototype.deref= function(){
    // remove leading and trailing quotes and spaces
    var obj= this.replace(/(^[' "]+|[" ']+$)/g,'');

    var M= obj.match(/(^[\w\$]+(\.[\w\$]+)*)/);
    if(M){
        M= M[1].split('.');
        obj= window[M.shift()];
        while(obj && M.length) obj= obj[M.shift()];
    }   
    return obj || this;
}

var getVar = function (obj) {
    for(var key in this) {
        if(obj === this[key]) return key;
    }
};

foo = 'foo';

console.log( getVar(foo) ); // => 'foo'

https://stackoverflow.com/a/17432007/1250044

If it's a global variable, you can look it up by name on the global object, since global variables are properties of the global object. On browsers, there's a global variable that refers to the global object called window, so:

var name = "foo";
window.foo = 42;
alert(Number(window[name])); // 42

But global variables are a Bad Thing^(tm).

To do this without globals, use your own object:

var name = "foo";
var obj = {};
obj.foo = 42;
alert(Number(obj[name])); // 42

Both of the above work because in JavaScript, you can refer to an object property either with dot notation and a literal (obj.foo), or with bracketed notation and a string (obj["foo"]), and in the latter case, the string can be the result of any expression, including a variable lookup.

You could use eval()