Looping JavaScript Arrays Using for, forEach & More 👨‍💻

Looping JavaScript Arrays Using for, forEach & More 👨‍💻

JavaScript has multiple iteration methods, starting with a traditional for loop and not the forEach method. Helper libraries like Lodash (forEach) and jQuery (each) can make it easier.

There are different ways to loop over arrays in JavaScript, but it can be difficult choosing the right one.

Plus keeping each method straight can drive a developer nuts.

There is a classic JavaScript for loop, JavaScript forEach method and a collection of libraries with forEach and each helper methods. And don't forget a JavaScript object is just a special array and you can iterate over its members as well.

You will learn different ways to loop or iterate JavaScript arrays, including how to use associative arrays or objects to find the values you want.

One of the most fundamental programming constructs is the for loop. All languages have some implementation of the for loop and forEach and JavaScript is no different.

As the language has matured so have our options to loop over arrays and objects. JavaScript objects are also arrays, which makes for a clean solution to index values by a key or name.

The Basic For Loop

JavaScript for loops iterate over each item in an array. JavaScript arrays are zero based, which means the first item is referenced with an index of 0.

Referencing items in arrays is done with a numeric index, starting at zero and ending with the array length minus 1. The syntax to access an array member

for (initialization; condition; final expression) { // code to be executed}

As you can see the for loop statement uses three expressions: the initialization, the condition, and the final expression. The final expression is executed at the end of each loop execution. It is commonly used to increment the index.

The following is an example of using JavaScript to loop through an array.

let myArray = ["one", "two", "three", "four"];
for(let i = 0; i < myArray.length; i++){ 
console.log(myArray[i]);
}

If you need to iterate through a second level property or field you can nest for loops. The biggest thing you need to keep track of is declaring a separate index variable.

let myArray = [{"child": ["one", "two", "three", "four"]}, 
{"child": ["five", "six", "seven", "eight"]}];
for(let i = 0; i < myArray.length; i++){ 
let childArray = myArray[i].child; 
for(let j = 0; j < childArray.length; j++){ 
console.log(childArray[j]); 
}
}/* Outputs:onetwothreefourfivesixseveneight*/

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