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Lodash _.every


Lodash is a popular JavaScript library with a wide range of useful utility functions. One such function is the _.every method. The purpose of this method is to determine whether all elements in a collection pass a specific condition or not.

The syntax for using _.every is straightforward. It takes two parameters: the collection (an array or object) and a function that evaluates each element in the collection. The function takes one argument, which is the current element being evaluated.

Here is an example of using _.every on an array of numbers:

const numbers = [1, 2, 3, 4, 5];
const areAllPositive = _.every(numbers, (num) => num > 0);
console.log(areAllPositive); // true

In this example, _.every checks if all elements in the numbers array are greater than 0. Since this condition is true for all elements, areAllPositive is set to true.

If any element fails the condition, _.every returns false. For example:

const numbers = [1, 2, 3, -4, 5];
const areAllPositive = _.every(numbers, (num) => num > 0);
console.log(areAllPositive); // false

In this case, the fifth element (-4) fails the condition, so areAllPositive is set to false.

_.every can also be used with objects. Here is an example:

const person = {
  name: "Alice",
  age: 30,
  occupation: "Engineer"

const isStringType = (value) => typeof value === "string";

const areAllStringProperties = _.every(person, isStringType);
console.log(areAllStringProperties); // false

In this example, _.every is used to check if all properties of the person object are strings. Since the age property is a number, areAllStringProperties is set to false.

_.every is a useful method when you need to check if an entire collection meets a certain condition. Keep in mind that _.every stops iterating as soon as an element fails the condition so it can be very performant.