7-closure.js

function f1(a) {
    let b = 2;
    setTimeout(function () {
        console.log(a, b)
    }, 1000);
}
// has a problem
// use let to scope variable inside for curly braces
function f2() {
    for (var i = 0; i < 3; i++) {
        setTimeout(function () {
            console.log(i)
        }, 1000 * i);
    }
}


function f3() {
    for (let i = 0; i < 3; i++) {
        setTimeout(function () {
            console.log(i)
        }, 1000 * i);
    }
}


function f4() {
    for (let i = 0; i < 3; i++) {
        setTimeout( (function (i) {
            console.log(x)
        }).bind(null,i), 1000 * i);// null is the context for the function, not important
    }
}