Trying to spread an array as arguments into the join method on path in node, but no luck:

var path = require("path");
var paths = [__dirname];
var userInput = ["app", "js"];
paths.push(userInput);
var target = path.join.apply(null, paths);

I get:

TypeError: Arguments to path.join must be strings

One possible solution is just give the method a string of arguments. I don't even know if that's possible. But just curious if there is a trick in JavaScript in situations like this. Or am I approaching it totally wrong ?

Trying to spread an array as arguments into the join method on path in node, but no luck:

var path = require("path");
var paths = [__dirname];
var userInput = ["app", "js"];
paths.push(userInput);
var target = path.join.apply(null, paths);

I get:

TypeError: Arguments to path.join must be strings

One possible solution is just give the method a string of arguments. I don't even know if that's possible. But just curious if there is a trick in JavaScript in situations like this. Or am I approaching it totally wrong ?

• javascript
• node.js

• I don't get this error. Is this your actual code? – Scimonster Commented May 6, 2015 at 3:36
• What is your desired output? – nnnnnn Commented May 6, 2015 at 3:39
• Can't repro either (Node v0.12) – Felix Kling Commented May 6, 2015 at 3:40
• I am reading values from the user with inquirer. Maybe I should rethink what I get from the user. I get path values like "app/js" and then split it into an array. And then I pass it to path.join to construct the path if that makes sense. – AJ Meyghani Commented May 6, 2015 at 3:42
• I will double check. Maybe I am doing something wrong with the input. Thanks for your comments. – AJ Meyghani Commented May 6, 2015 at 3:43

2 Answers 2

You are pushing an array onto an array, resulting in

[ __dirname, [ 'app', 'js' ] ]

path.join has no idea what to do with these nested arrays. apply does not somehow magically flatten its input. The error message from path.join could not be clearer: it wants its arguments to be strings, not arrays. So instead use concat to combine the arrays:

var path = require("path");
var paths = [__dirname];
var userInput = ["app", "js"];

// Use concat here
paths = paths.concat(userInput);

var target = path.join.apply(null, paths);

An alternative would be

paths.push.apply(paths, userInput);

which would push the elements of userInput onto paths one by one.

If you are using ES6, then you could use the spread operator and write this as:

paths.push(...userInput)

or

paths = [...paths, ...userInput]

or just directly

var target = path.join(...paths, ...userInput)

Actually the issue was that I was overthinking the problem. Instead of concatenating the paths array with the other array, I was pushing an array into the paths array:

var path = require("path");
var paths = [__dirname];
var userInput = ["app", "js"];
paths.push(userInput); // x

The problem can be avoided by just paths.concat(userInput). Then you can spread the arguments:

path.join.apply(null, paths.concat(userInput));

Thanks to @torazaburo for pointing it out.