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.