strict-extend

A shallow extend method that removes extra properties from the target object.

Inspired by jQuery's .extend() and Object.assign(), but any properties on the target argument that aren't on any of the source arguments will be removed. Useful for filling in defaults for options parameters.

Installation

This package is available on npm as strict-extend.

npm install strict-extend

Usage

Syntax

strictExtend(target, ...sources)

Parameters

target: The target object.

sources: The source object(s).

Description

strictExtend will return a new object containing all of the properties from all of the sources object(s). Any properties already present on target will not be overwritten. However, any properties present on target which are not present on any of the sources object(s) will not be copied to the return object. Values for properties which are on multiple sources objects will be resolved by taking the value from the last source object.

Note that an error will not be thrown for null or undefined parameters. Instead, an empty object will be returned.

Examples

Default Options

import strictExtend from 'strict-extend'; // or const strictExtend = require('strictExtend');
 
const defaults = {
    color: 'red',
    name: 'Clifford',
};
 
function dog(options) {
    return strictExtend(options, defaults);
}
 
console.log(dog()); // { color: 'red', name: 'Clifford' }
console.log(dog({ color: 'blue', name: 'Sparky'})); // { color: 'blue', name: 'Sparky' }
console.log(dog({ name: 'Rover', hasCollarOn: true })); // { color: 'red', name: 'Rover' }
// 'hasCollarOn' was ignored

Multiple Sources and Last In Behavior

const strictExtend = require('strict-extend') // or import strictExtend from 'strict-extend';
 
const target = {
    kept: 'should not be overwritten',
    removed: 'should NOT be copied'
};
const source1 = {
    kept: 'this will be ignored',
    newProp1: 'this will be copied',
    newProp2: 'this value will be ignored due to the property on source2'
};
const source2 = {
    newProp2: 'last in wins!'
};
console.log(strictExtend(target, source1, source2));
//  {
//      kept: 'should not be overwritten', (copied from target)
//      newProp1: 'this will be copied', (copied from source1)
//      newProp2: 'last in wins!', (copied from source2)
//  }
//  notice 'removed' from target not copied

null/undefined Behavior

import strictExtend from 'strict-extend';
console.log(strictExtend()); // {}
console.log(strictExtend(null)); // {}
console.log(strictExtend(null, null)); // {}
console.log(strictExtend({}, null )); // {}
console.log(strictExtend(null, {})); // {}

Development

Install

1. Clone the repository.
2. Run npm install in the directory you cloned into.

Tests

npm test assumes you have Chrome and Firefox installed. If that is not the case, you can run npm run test-ci to only run tests with PhantomJS (which is a dev dependency). Or, you can run the tests and specify which browsers you'd like to test with using the --browsers option with karma start. For example, to test only with Firefox, you can run karma start --browsers Firefox.

License

Licensed under the MIT License.