Author: John Au-Yeung

To initialize an array’s length in JavaScript, we set the array’s length property.

For instance, we write

const test = [];
test.length = 4;

to set the length property of the test array to set its length to 4.

To split array into chunks with JavaScript, we use a for loop.

For instance, we write

const chunkSize = 10;
for (let i = 0; i < array.length; i += chunkSize) {
  const chunk = array.slice(i, i + chunkSize);
  //...
}

to use a for loop to loop through i from 0 to the array‘s length minus 1.

We increment i by the chunkSize in each iteration.

In the loop, we call array.slice with i and i + chunkSize to return the slice of the array between index i and i + chunkSize - 1 as a new array.

To get first N number of elements from an array with JavaScript, we use the slice method.

For instance, we write

const slicedArray = array.slice(0, n);

to call array.slice with 0 and n to return the first n items in the array array in a new array.

To access and process nested objects, arrays, or JSON with JavaScript, we use object methods.

For instance, we write

const obj = {
  a: 1,
  b: 2,
  c: 3,
};

console.log(Object.keys(obj));
console.log(Object.values(obj));
console.log(Object.entries(obj));

to call Object.keys to get the property keys of obj in an array.

We call Object.values to get the property values of obj in an array.

And we call Object.entries to get the property key-value pair arrays in obj in an array.

To copy array items into another array with JavaScript, we use the concat function.

For instance, we write

const arrayA = [1, 2];
const arrayB = [3, 4];
const newArray = arrayA.concat(arrayB);

to call arrayA.concat with arrayB to return a new array with arrayA‘s contents with arrayB‘s contents being it.