Like Object.assign, but key/value assigning is determined by a predicate function
npm install assign-where --saveassignWhere( predicate, target, [sources]);
Arguments:
predicate(function): Takes an array[key, value], and returns bool, This determins if each enumerable key/value should be assigned totargettarget(enumerable): The value to be assigned onto (to be mutated)[sources](enumerables): The source values
NOTE: Like Object.assign, assignWhere will attempted to coerce target and sources to objects
import assignWhere from 'assign-where';
const target = { existing: 'here'};
const output = assignWhere(
([key, value]) => key.startsWith('a'),
target,
{ apple: 'Manzana'},
{ bannana: 'Banano'},
{ crab: 'crangrejo'}
);
console.log(output);
// { existing: "here", apple: "Manzana" }
console.log(target === output);
// trueimport assignWhere from 'assign-where';
const target = { existing: 'here'};
const output = assignWhere(
([key, value]) => value.endsWith('o'),
target,
{ apple: 'Manzana'},
{ bannana: 'Banano'},
{ crab: 'crangrejo'}
);
console.log(output);
// { existing: "here", bannana: "Banano", crab: "crangrejo" }
console.log(target === output);
// trueUse in-built functions
let target = { existing: 'here'};
Object
.entries(
Object.assign(
{ apple: 'Manzana'},
{ bannana: 'Banano'},
{ crab: 'crangrejo'}
)
).filter(
([key, value]) => value.endsWith('o')
).forEach(
([key, value]) => target[key] = value
);
console.log(target);
// { existing: "here", bannana: "Banano", crab: "crangrejo" }The initial use case was in React, wanting to examine a Component's props and find all the custom data attributes data-.
const dataAttr = ([k,v]) => k.startsWith('data-')
const MyComp = props =>
<div
{...assignWhere(dataAttr, props)}
>
<h1>{props.heading}</h1>
<p>{props.content}</p>
</div>
ReactDOM.render(
<MyComp data-test data-x data-y />,
document.getElementById('root')
);
document.querySelector('[data-test]']); // Works- Based on
Object.assign(targetis mutated), andArray.filter sourcesofnullandundefinedare ignored (likeObject.assign)predicateparams based on output ofObject.entries- Uses rollupjs & babeljs to build a commonjs module
bundle.jsfromsrc/main.js
npm testnpm run dev
npm run build
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