Page 93 - JavaScript

In ES 6, the for-of loop is the recommended way of iterating over a the values of an array:

6

let myArray = [1, 2, 3, 4];
for (let value of myArray) {
let twoValue = value * 2;
console.log("2 * value is: %d", twoValue);
}

The following example shows the difference between a for...of loop and a for...in loop:

6

let myArray = [3, 5, 7];
myArray.foo = "hello";

for (var i in myArray) {
console.log(i); // logs 0, 1, 2, "foo"
}

for (var i of myArray) {
console.log(i); // logs 3, 5, 7
}

Array.prototype.keys()

The Array.prototype.keys() method can be used to iterate over indices like this:

6

let myArray = [1, 2, 3, 4];
for (let i of myArray.keys()) {
let twoValue = myArray[i] * 2;
console.log("2 * value is: %d", twoValue);
}

Array.prototype.forEach()

The .forEach(...) method is an option in ES 5 and above. It is supported by all modern browsers,
as well as Internet Explorer 9 and later.

5

[1, 2, 3, 4].forEach(function(value, index, arr) {
var twoValue = value * 2;
console.log("2 * value is: %d", twoValue);
});

Comparing with the traditional for loop, we can't jump out of the loop in .forEach(). In this case,
use the for loop, or use partial iteration presented below.

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