What is the use of underscore ( _ ) in JavaScript?
Underscore (_) is just a character that has no special meaning in JavaScript. But it can be used for different purposes.
Use of underscore (_) in JavaScript
Here are some of the uses of underscore in JavaScript:
1. Variable name spacing
The most common use of an underscore in JavaScript is to give space to a variable name, which makes it easier to understand what a variable is all about. For example, var my_variable = 10;.
2. Ignoring function parameters
Underscore can be used for ignoring function parameters. For example, you may define a function that requires parameters, but you don’t intend to use all of them at that time.
In such cases, you can use an underscore as a convention to indicate that the parameter is intentionally being ignored.
It’s a way to communicate to other developers that the parameter value is not relevant to the function’s logic.
function exampleFunc(_, b) {
// The first parameter (_) is ignored
console.log(b);
}
exampleFunc('ignored', 'used');
// Output: "used"
Ignoring value when calling functions
When calling functions that return multiple values, you can use an underscore to ignore values that you don’t need from the functions.
function getCoordinates() {
// Simulating a function that returns an array of coordinates
return [10, 20, 30];
}
const [x, y, _] = getCoordinates();
console.log(x, y);
// Output: 10 20
Library or framework conventions
Some JavaScript libraries or frameworks, like Underscore.js or Lodash, use the underscore as part of their naming conventions.
These libraries provide utility functions for working with arrays, objects, and other data types.
For example, in Underscore.js, you can transform an array into a new array using the functions or methods it provides like filter and map.
Here is a code snippet that use Underscore.js map method to double the value of the numbers in an array.
_.map([1, 2, 3], function(num) {
return num * 2;
});
// Output: [2, 4, 6]
Though, the map method in the code above was used to transform the array [1, 2, 3] into [2, 4, 6] by multiplying [1, 2, 3] by 2.
This way of transforming or mapping an array into a new array was done using the underscore.js library.
In today’s modern ES6 JavaScript, there are inbuilt functions/method like map() and filter() that comes with JavaScript, which makes the use of underscore.js quite obsolete.
Read on: Difference Between map() and filter() in JavaScript With Example
In Few Points:
The use of _ in JavaScript is to give space to a variable name, to ignore a function parameter, and it is also used in a library like underscore.js to transform arrays and object.
