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I would like to use the reduce function instead of doing this:

var result = '';
authors.forEach(
    function(author) {
        result += author.name + ', ';
    }
);
console.log(result);

So in the array authors there are several names. Now I want to build a string with this names, separated by comma (except the last one).

var result = authors.reduce(function (author, index) {
    return author + ' ';
}, '');
console.log(result);

I would like to use the reduce function instead of doing this:

var result = '';
authors.forEach(
    function(author) {
        result += author.name + ', ';
    }
);
console.log(result);

So in the array authors there are several names. Now I want to build a string with this names, separated by comma (except the last one).

var result = authors.reduce(function (author, index) {
    return author + ' ';
}, '');
console.log(result);

• javascript
• underscore.js

Share Improve this question Follow asked Jul 8, 2016 at 15:13 user3142695user3142695 17.3k5555 gold badges194194 silver badges372372 bronze badges 1

• If you want to use reduce or a loop for some reason, you have to add a check to see if the current loop element is the last one or not. But just use join, it's one line of code to get what you want. – Shilly Commented Jul 8, 2016 at 15:15

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7 Answers 7

Sorted by: Reset to default 163

A flurry of answers just came in and here is one more!

The first option is using the native js join method which eliminates the need for reduce. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join

var authors = ['some author', 'another author', 'last author'];
var authorString = authors.join(",");
console.log(authorString);

IMPORTANT - if you're array contains objects, then you might want to map it before joining:

var authors = [{name: 'some author'},{name: 'another author'},{name: 'last author'}]
var authorString = authors.map(function(author){
    return author.name;
}).join(",");
console.log(authorString);

or, if you're really fired up about using reduce, just make sure you use the previous value, current value and index when passing in the callback. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

var authorString = authors.reduce(function(prevVal,currVal,idx){
    return idx == 0 ? currVal : prevVal + ', ' + currVal;
}, '')
console.log(authorString);

IMPORTANT - again if your array contains objects then you will want to make sure you are using the 'name property':

var authors = [{name: 'some author'},{name: 'another author'},{name: 'last author'}];
var authorString = authors.reduce(function(prevVal,currVal,idx){
    return idx == 0 ? currVal.name : prevVal + ', ' + currVal.name;
}, '')
console.log(authorString);

Right, so it's an object. Let's map the names first then:

var result = authors.map(function( author ) {
    return author.name;
}).join(', ');

You are reinventing join()

var authors = ["a","b","c"];
var str = authors.join(", ");
console.log(str);

if you want to use reduce add an if check

var authors = ["a","b","c"];

var result = authors.reduce(function (author, val, index) {
    var comma = author.length ? ", " : "";
    return author + comma + val;
}, '');
console.log(result);

---

Since I missed the mapping part to make people happy...

var authors = [{
  name: "a"
}, {
  name: "b"
}, {
  name: "c"
}];

var res = authors.map( function(val) { return val.name; }).join(", ");
console.log(res);

OR

var authors = [{
  name: "a"
}, {
  name: "b"
}, {
  name: "c"
}];
var result = authors.reduce(function(author, val, index) {
  var comma = author.length ? ", " : "";
  return author + comma + val.name;
}, '');
console.log(result);

I came across this also. Most of these answers dont take into account that you want the authors name, meaning you have an array of objects.

A one line solution:

authors.reduce((prev, curr) => [...prev, curr.name], []).join(', ');

Try this:

var authors = ["Mikel", "Brad", "Jessy", "Pof", "MArting"]
var result = authors.reduce( (prev, curr) => prev +', '+ curr )

console.log(result)

I will add my 2 cents, two options here, either through map or using ternary operator:

const authors = [{name: 'John'}, {name: 'Jack'}, {name: 'Charles'}];

// Map
const reducedMap = authors.map(a => a.name).reduce((result, name) => `${result},${name}`);

// Ternary operator and initial value
const reducedTernary = authors.reduce((result, author) => `${result}${result ? ',' : ''}${author.name}` , '');

// Result :
// John,Jack,Charles

Here is a "Python Like" method to build a string in one line using an array or an Object.

// From an Array
['Hey', 'Hi', 'Hello!'].reduce((result, item, index) => (index !==0 ? `${result}, `: '')+`${item}`, '')


// From an Object
Object.entries({one: 1, two: 2, three: 3}).reduce((result, [key, value], index) => (index !==0 ? `${result}, `: '')+`${key} -> ${value}`, '')

I hope this helps. Cheers.

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