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To use the spread operator to update an object value with JavaScript, we use the spread operator in a new object. const o2 = { ... o1, a: "updated a" }; console. log(o2);
let array = [{id:1,name:'One'}, {id:2, name:'Two'}, {id:3, name: 'Three'}]; let array2 = array. map(a => { var returnValue = {...a}; if (a.id == 2) { returnValue.name = "Not Two"; } return returnValue }) console. log(array); console.
Spread syntax can be used when all elements from an object or array need to be included in a new array or object, or should be applied one-by-one in a function call's arguments list. There are three distinct places that accept the spread syntax: Function arguments list ( myFunction(a, ...
The properties are added in order, so if you want to override existing properties, you need to put them at the end instead of at the beginning:
return {
value: {
...initialState,
...newObject
}
}
You don't need newObject (unless you already have it lying around), though:
return {
value: {
...initialState,
isAvailable: newValue
}
}
Example:
const o1 = {a: "original a", b: "original b"};
// Doesn't work:
const o2 = {a: "updated a", ...o1};
console.log(o2);
// Works:
const o3 = {...o1, a: "updated a"};
console.log(o3);If you know the name of the property (a in the example below), then @crowder's answer is perfect:
const o3 = {...o1, a: "updated a"};
console.log(o3);
If the property name is in a variable, then you need to use Computed Property names syntax:
let variable = 'foo'
const o4 = {...o1, [variable]: "updated foo"};
console.log(o4);
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