How to use the assignWith function from lodash

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

lodash.assignWith is a function in the Lodash library that copies the values of all enumerable properties from one or more source objects to a target object while allowing customization of how values are assigned.

lodash-contrib.commonjs.js

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module.exports.arity               = _.arity;
module.exports.ary                 = _.ary;
module.exports.assign              = _.assign;
module.exports.assignIn            = _.assignIn;
module.exports.assignInWith        = _.assignInWith;
module.exports.assignWith          = _.assignWith;
module.exports.at                  = _.at;
module.exports.attempt             = _.attempt;
module.exports.before              = _.before;
module.exports.best                = _.best;

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+ 92 other calls in file

lodash.js

GitHub: mdmarufsarker/lodash

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console.log(assignIn); // => { 'a': 1, 'b': 2, 'c': 3 }


const assignInWith = _.assignInWith({ 'a': 1 }, { 'b': 2 }, { 'c': 3 }, (a, b) => a + b);
console.log(assignInWith); // => { 'a': 1, 'b': 2, 'c': 3 }


const assignWith = _.assignWith({ 'a': 1 }, { 'b': 2 }, { 'c': 3 }, (a, b) => a + b);
console.log(assignWith); // => { 'a': 1, 'b': 2, 'c': 3 }


const at = _.at({ 'a': [{ 'b': { 'c': 3 } }, 4] }, ['a[0].b.c', 'a[1]']);
console.log(at); // => [3, 4]

+ 15 other calls in file

How does lodash.assignWith work?

lodash.assignWith works by taking in two or more objects as arguments, with the first argument being the target object that will receive the properties and values from the other source objects. For each property in the source objects, lodash.assignWith checks whether the property already exists in the target object. If the property does not exist, it is added to the target object with its corresponding value. If the property already exists in the target object, the customizer function is called to determine the value of the property in the target object. The customizer function is an optional argument that can be provided to lodash.assignWith. It takes four arguments: the current value in the target object, the value from the source object, the property key, and the target object itself. The customizer function returns the value that should be assigned to the property in the target object. If no customizer function is provided, the default behavior is to simply assign the value from the source object to the property in the target object. After iterating over all the properties in the source objects, lodash.assignWith returns the target object with all the copied properties and values.

model.js

GitHub: sequelize/sequelize

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    this._expandIncludeAll(include, include.model);
  }
}

static _baseMerge(...args) {
  _.assignWith(...args);

  return args[0];
}

+ 7 other calls in file

Ai Example

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const _ = require("lodash");

// Define the target object
const target = { a: 1, b: 2 };

// Define a source object
const source = { b: 3, c: 4 };

// Define a customizer function to add values
const customizer = (targetValue, sourceValue, key, targetObject) => {
  if (_.isUndefined(targetValue)) {
    return sourceValue; // Add new values to the target object
  }
  return targetValue + sourceValue; // Add values together if they already exist in the target object
};

// Use lodash.assignWith to copy properties and values from the source object to the target object
const result = _.assignWith(target, source, customizer);

console.log(result); // Output: { a: 1, b: 5, c: 4 }

In this example, we start with a target object that has two properties (a and b). We also have a source object that has two properties (b and c). When we use lodash.assignWith, we provide a customizer function that determines how values should be assigned. In this case, the customizer function checks whether the property already exists in the target object. If it does not exist (targetValue is undefined), the customizer function returns the value from the source object. If the property already exists in the target object, the customizer function adds the values together (targetValue + sourceValue). The result is a new object with all the properties and values from both the target and source objects. The b property has a value of 5 because the value from the source object (3) was added to the value already in the target object (2). The c property was added to the target object because it did not exist before.

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