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Lodash _.once() Method
  • Last Updated : 29 Sep, 2020

Lodash is a JavaScript library that works on the top of underscore.js. Lodash helps in working with arrays, strings, objects, numbers, etc.

The _.once() method of Function in lodash is used to create a function which can call func parameter of this method only once. However, repeated calls to this function will return the value returned in the first call. 

Note: The func parameter of this method is called with this binding along with the arguments of the created function.

Syntax:

_.once(func)

Parameters: This method accepts a single parameter which is described below:



  • func: It is the function which is to be restricted.

Return Value: This method returns the new restricted function.

Example 1:

Javascript

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// Requiring lodash library
const _ = require('lodash');
  
// Calling once() method with its parameter
var hold = _.once(function(trap){
   console.log(trap + '!');
});
  
// Calling hold multiple times
hold('Logged in to the console');
hold('GfG');
hold('CS');

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Output:

Logged in to the console!

Here, hold is called multiple times but only the value of first call is returned as you can call func only once as stated above.

Example 2:

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// Requiring lodash library
const _ = require('lodash');
  
// Calling once() method with its parameter
var fetch = _.once(function(value){
   return value;
});
  
// Calling fetch multiple times
console.log(fetch(1013));
console.log(fetch(1014));

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Output:

1013
1013

Here, each time the fetch is called the same value is returned as returned to the first call.

Reference: https://lodash.com/docs/4.17.15#once

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