Question

I’m trying get value of var by its name:

var1='Hello'

var2 = getTextFromFirstTextBox() //text in label is "var1"

var3 = ${var2}

Everything works, but here I should get ‘hello’ but it doesn’t work

var4 = ${var3} 

What I must to do to set value of value1 to value4?

Answer 1

Let’s take this one line from your question:

var1='Hello'

As it stands, that will create a global variable (regardless of where the code is). Global variables are properties of the global object, which is window on browsers, so you can access that via bracketed notation with a string (e.g., window["var1"]) as a couple of the answers here mention. But that’s only part of the story.

If the code is at global scope, it’s fairly obvious you’re creating a global variable. If that line appears as-is in a function, it still creates a global variable — you’re falling prey to the Horror of Implicit Globals.

The moral of the story is: Use var when creating variables:

var var1 = 'Hello';

Now you’re explicitly creating a variable in the current scope — e.g., at global scope if that’s where the code is, or at function scope if that’s where the code is.

So global variables are properties of window; how ’bout function variables, are they properties of an object? Yes, they are (it’s called the “variable object” in the spec, and it’s a very real thing, not a spec abstraction), but you have no means of accessing that object directly, there’s no symbol or name you can use to get at it. If you want to get a function’s variable using a string version of its name, your only option is eval, and don’t do that. Instead, refactor the code and make the thing you need to access the property of an object:

var thingsToLookUp = {
    var1: "Hello",
    var2: "There"
};
alert(thingsToLookUp["var1"]); // alerts "Hello"