Stringifying all array content with .map function

Question

Why is this not working?

var numbers = [1,2,3,4,5,6,7,8];
var stringifiedNumbers = numbers.map(function(x) { 
   JSON.stringify(x);
})
console.log(stringifiedNumbers);

Why is my output:

Array [ undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined ]

Also seems total overkill to use JSON.stringify for a simple numeric. Just use return x.toString() — Jamiec
– Jamiec, Commented May 11, 2017 at 12:21

Andrew Li · Accepted Answer · 2017-05-12 22:12:20Z

5

You're not returning the stringified content so the function transforms the array into undefineds. Array#map transforms each array element based on the return value of the passed callback and since yours returns nothing it transforms them to undefined:

var numbers = [1, 2, 3, 4, 5, 6, 7, 8];
var stringifiedNumbers = numbers.map(function(x) {
  return JSON.stringify(x);
})
console.log(stringifiedNumbers);

You could shorten this with arrow functions:

var stringifiedNumbers = numbers.map(x => JSON.stringify(x));

Because you are only using one return statement in the example above, you can implicitly return the expression with an arrow function. You could even just shorten it to:

numbers.map(JSON.stringify);

As it implicitly passes the argument and gets rid of the variable.

edited May 12, 2017 at 22:12

answered May 11, 2017 at 12:19

Andrew Li

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