Array | Ucode

Appearance

On this page

Array ​

In addition to methods like map(), reduce(), filter(), and sort(), the Array object provides many other useful higher-order functions.

Every ​

The every() method checks if all elements in the array satisfy a given test condition. For example, to check if all strings in an array are non-empty:

javascript
let arr = ['Apple', 'pear', 'orange'];
console.log(arr.every(function (s) {
    return s.length > 0;
})); // true, because all elements satisfy s.length > 0

console.log(arr.every(function (s) {
    return s.toLowerCase() === s;
})); // false, because not all elements are lowercase

Find ​

The find() method is used to locate the first element that meets the specified condition. If found, it returns that element; otherwise, it returns undefined:

javascript
let arr = ['Apple', 'pear', 'orange'];
console.log(arr.find(function (s) {
    return s.toLowerCase() === s;
})); // 'pear', because 'pear' is entirely lowercase

console.log(arr.find(function (s) {
    return s.toUpperCase() === s;
})); // undefined, because there is no element that is entirely uppercase

FindIndex ​

Similar to find(), the findIndex() method locates the first element that meets the condition but returns the index of that element. If none is found, it returns -1:

javascript
let arr = ['Apple', 'pear', 'orange'];
console.log(arr.findIndex(function (s) {
    return s.toLowerCase() === s;
})); // 1, because the index of 'pear' is 1

console.log(arr.findIndex(function (s) {
    return s.toUpperCase() === s;
})); // -1, because there is no all-uppercase element

ForEach ​

The forEach() method is similar to map(), applying the given function to each element but not returning a new array. It is commonly used for traversing arrays, so the function passed does not need to return a value:

javascript
let arr = ['Apple', 'pear', 'orange'];
arr.forEach(x => console.log(x)); // Prints each element in order