How eval in JavaScript changes the calling context?

Question

On dynamic property of JavaScript is that "eval" changes the calling context. What does it mean? Some examples would be better.

Answer 1

eval does change the context when called indirectly. And it changes it to the global context (the default context for all functions).

var myObj = { a: 1 }

function someFunc() {
    console.log(eval('this.a')) // 1
    console.log(eval('this === myObj')) // true

    var indirectEval = eval

    console.log(indirectEval('this.a')) // undefined
    console.log(indirectEval('this === window')) // true
}

void someFunc.call(myObj)

Direct eval calls don't change the context (nor do they change the scope).

See “Global eval. What are the options?” for details.