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How to use the once function from lodash

Find comprehensive JavaScript lodash.once code examples handpicked from public code repositorys.

lodash.once is a utility function from the Lodash library that creates a new function that can only be called once, and then returns the result of that initial call on all subsequent calls.

astrobench.js

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* @category Functions
* @param {Function} func The function to restrict.
* @returns {Function} Returns the new restricted function.
* @example
*
* var initialize = _.once(createApplication);
* initialize();
* initialize();
* // `initialize` executes `createApplication` once
*/

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lodash-contrib.commonjs.js

GitHub: node4good/lodash-contrib

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module.exports.nthArg              = _.nthArg;
module.exports.nths                = _.nths;
module.exports.omit                = _.omit;
module.exports.omitBy              = _.omitBy;
module.exports.omitWhen            = _.omitWhen;
module.exports.once                = _.once;
module.exports.orderBy             = _.orderBy;
module.exports.over                = _.over;
module.exports.overArgs            = _.overArgs;
module.exports.overEvery           = _.overEvery;

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+ 92 other calls in file

How does lodash.once work?

lodash.once works by creating a new function that can only be called once, and then returning the result of that initial call on all subsequent calls. When the new function created by lodash.once is called for the first time, it invokes the original function with the arguments provided, and saves the result. Subsequent calls to the function return the saved result without invoking the original function again. This behavior can be useful in situations where a function's output will not change after it has been called once, or where repeated calls to the function may be expensive or time-consuming. Note that lodash.once is part of the Lodash library, which provides a set of tools and utilities for working with arrays, objects, and functions in JavaScript.

production-start.js

GitHub: iamirulofficial/freeCodeCamp

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const app = require('./server');

let timeoutHandler;
let killTime = 15;

const onConnect = _.once(() => {
  log('db connected in: %s', Date.now() - startTime);
  if (timeoutHandler) {
    clearTimeout(timeoutHandler);
  }

+ 3 other calls in file

lodash.js

GitHub: mdmarufsarker/lodash

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console.log(memoize(1, 2)); // => 3


const negate = _.negate(n => n > 0);
console.log(negate(1)); // => false


const once = _.once(() => console.log('hello'));
once();


const overArgs = _.overArgs((x, y) => [x, y], [n => n + 1, n => n + 2]);
console.log(overArgs(1, 2)); // => [2, 4]

+ 15 other calls in file

Ai Example

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const _ = require("lodash");

function expensiveOperation() {
  console.log("Performing expensive operation...");
  return 42;
}

const performOnce = _.once(expensiveOperation);

console.log(performOnce()); // Performing expensive operation... 42
console.log(performOnce()); // 42
console.log(performOnce()); // 42

In this example, we define a function called expensiveOperation that logs a message to the console and returns a constant value (42). We then use lodash.once to create a new function called performOnce that can only be called once. We pass expensiveOperation as an argument to _.once, which creates a new function that will invoke expensiveOperation on its first call and save the result. We then call performOnce three times in a row, and observe that the message "Performing expensive operation..." is only logged once, while the result 42 is returned on all subsequent calls. Note that lodash.once can be used with any function, including functions that take arguments, and can be customized with additional options such as a before function to be called before the first invocation, or a after function to be called after the final invocation.

utils.js

GitHub: electrode-io/electrode

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  } else {
    return Boom.internal();
  }
}


const checkSSRMetricsReporting = _.once(topOpts => {
  const reporting = _.get(topOpts, "reporting", {});
  if (!reporting.enable || !reporting.reporter) {
    // eslint-disable-next-line
    console.log(

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+ 8 other calls in file

sign.js

GitHub: tanverhasanre/jsonwebtoken_tool

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});

const encoding = options.encoding || 'utf8';

if (typeof callback === 'function') {
  callback = callback && once(callback);

  jws.createSign({
    header: header,
    privateKey: secretOrPrivateKey,

ProjectController.js

GitHub: overleaf/overleaf

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  return callback(null, user)
}
// If the refresh takes too long then return the current
// features. Note that the user.features property may still be
// updated in the background after the callback is called.
callback = _.once(callback)
const refreshTimeoutHandler = setTimeout(() => {
  req.session.feature_refresh_failed = { reason: 'timeout', at: new Date() }
  metrics.inc('features-refresh', 1, {
    path: 'load-editor',

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db.js

GitHub: askulysh/rmd

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const { minimizePath } = require("./helpers");


let CACHE = null;
const PATH = path.join(process.cwd(), "../REC_DB.json");


const startDb = _.once(async () => {
  try {
    try {
      await fs.promises.access(PATH, fs.constants.R_OK | fs.constants.W_OK);
      CACHE = JSON.parse(await fs.promises.readFile(PATH, "utf8"));

+ 11 other calls in file

DockerRunner.js

GitHub: overleaf/overleaf

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    }
  })
},

_runAndWaitForContainer(options, volumes, timeout, _callback) {
  const callback = _.once(_callback)
  const { name } = options

  let streamEnded = false
  let containerReturned = false

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+ 5 other calls in file

run.js

GitHub: sindeshiva/Test

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})


const createVideoRecording = function (videoName, options = {}) {
  const outputDir = path.dirname(videoName)


  const onError = _.once((err) => {
    // catch video recording failures and log them out
    // but don't let this affect the run at all
    return errors.warning('VIDEO_RECORDING_FAILED', err.stack)
  })

functiondemo.js

GitHub: Hupeng7/es6demo

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let negate1 = _.filter([1, 2, 3, 4, 5, 6], _.negate(isEven));
console.log('negate1--->', negate1);
//negate1---> [ 1, 3, 5 ]


//_.once(func)
// var initialize = _.once(createApplication);
// initialize();
// initialize();
//

+ 3 other calls in file

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