How Can I Efficiently Iterate Through Arrays and Array-like Objects in JavaScript?

Looping Through Arrays in JavaScript

In JavaScript, there are various ways to iterate through the elements of an array:

Looping Over Genuine Arrays

• For-of Loop (ES2015 ):

for (const element of theArray) {
    // Use `element`...
}

• forEach (ES5 ):

theArray.forEach(element => {
    // Use `element`...
});

• Simple For Loop:

for (let index = 0; index < theArray.length; ++index) {
    const element = theArray[index];
    // Use `element`...
}

• For-in (with Safeguards):

for (const propertyName in theArray) {
    if (/*...is an array element property (see below)...*/) {
        const element = theArray[propertyName];
        // Use `element`...
    }
}

Looping Over Array-like Objects

• For-of Loop (ES2015 ):

for (const element of arrayLike) {
    // Use `element`...
}

• forEach (ES5 ):

arrayLike.forEach(element => {
    // Use `element`...
});

• Simple For Loop (with Caution):

for (let index = 0; index < arrayLike.length; ++index) {
    // Note: `arrayLike.length` may not be reliable.
    if (arrayLike.hasOwnProperty(index)) {
        const element = arrayLike[index];
        // Use `element`...
    }
}

• Array.from and For-of Loop:

const arrayLikeItems = Array.from(arrayLike);
for (const element of arrayLikeItems) {
    // Use `element`...
}

Recommendations

• For genuine arrays, use the for-of loop or forEach if your callback is a simple synchronous function.
• For array-like objects, use the for-of loop with caution, and consider using Array.from() to create a genuine array first for greater reliability.

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