Error calling forEach on an array literal in javascript

Question

This code generates an error when I run it with node v6.9.2

var req = {}

[\'foo\', \'bar\'].forEach(prop => {
    console.log(\"prop: \" + prop)
});
         


        

Answer 1

Automatic semicolon insertion has turned

var req = {}
['foo', 'bar']

into

var req = {}['foo', 'bar']

and of course {} doesn't contain a 'bar' property (because 'foo', 'bar' evaluates to 'bar').

(undefined).forEach(...) gets evaluated, which then leads to the error that you're seeing.

---

If you're relying on ASI, it's common practice to prefix lines beginning with [] or () with a semicolon:

var req = {}
;['foo', 'bar']