So basically, I have an array of objects and I'd like to update only the objects in the array that satisfy a condition. I want to know if there's like a good functional way of solving that problem. Right now I'm using lodash. Here's and example:

var things = [
    {id: 1, type: "a", value: "100"}, 
    {id: 2, type: "b", value: "300"}, 
    {id: 3, type: "a", value: "100"}
];
var results = _.map(things, function (thing) { 
    if(thing.type === "a") {
        thing.value = "500";
    } 
    return thing;
});
// => results should be [{id: 1, type: "a", value: "500"}, {id: 2, type: "b", value: "300"}, {id: 3, type: "a", value: "500"}];

So basically, I have an array of objects and I'd like to update only the objects in the array that satisfy a condition. I want to know if there's like a good functional way of solving that problem. Right now I'm using lodash. Here's and example:

var things = [
    {id: 1, type: "a", value: "100"}, 
    {id: 2, type: "b", value: "300"}, 
    {id: 3, type: "a", value: "100"}
];
var results = _.map(things, function (thing) { 
    if(thing.type === "a") {
        thing.value = "500";
    } 
    return thing;
});
// => results should be [{id: 1, type: "a", value: "500"}, {id: 2, type: "b", value: "300"}, {id: 3, type: "a", value: "500"}];

• javascript
• dictionary
• functional-programming
• lodash

Share Follow asked Nov 10, 2017 at 22:13 LynchburgExplorerLynchburgExplorer 72088 silver badges99 bronze badges

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4 Answers 4

Sorted by: Reset to default 4

There is no need here to use map method.

You can use a simply forEach function by passing a callback function to it.

var results = _.forEach(things, function (thing) { 
  if(thing.type === "a") {
    thing.value = "500";
  } 
});

You could just map the new objects with a condition inside of Object.assign, without mutating the original object.

var things = [{ id: 1, type: "a", value: "100" }, { id: 2, type: "b", value: "300" }, { id: 3, type: "a", value: "100" }],
    results = things.map(o => Object.assign({}, o, o.type === "a" && { value: 500 }));

console.log(results);

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You can use Array#map (or Lodash's equivalent) with a ternary that will create a new updated object if the type is a using Object#assign:

var things = [
    {id: 1, type: "a", value: "100"}, 
    {id: 2, type: "b", value: "300"}, 
    {id: 3, type: "a", value: "100"}
];
var result = things.map(function (thing) { 
    return thing.type === 'a' ? Object.assign({}, thing, { value: 500 }) : thing;
});

console.log(result);

This is perhaps a little early, but with the proposal for object rest spread which is currently in stage-3 you could solve it like this:

const things = [
    {id: 1, type: "a", value: "100"}, 
    {id: 2, type: "b", value: "300"}, 
    {id: 3, type: "a", value: "100"},
];
const result = things.map(e => e.type === 'a' ? {...e, value: 500 } : e);
console.log(result);