Node: strange behaviour of [] in start of the line

[pvinis]

Version: v7.9.0
Platform: Darwin green.local 16.5.0 Darwin Kernel Version 16.5.0: Fri Mar 3 16:52:33 PST 2017; root:xnu-3789.51.2~3/RELEASE_X86_64 x86_64

so i have this in a file

console.log('hello')

const a = 2

[3,4].forEach(n => console.log(n))

and when doing node weird.js i get

[3,4].forEach(n => console.log(n))
     ^

TypeError: Cannot read property 'forEach' of undefined
    at Object.<anonymous> (/Users/pvinis/Desktop/weird.js:3:6)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:423:7)
    at startup (bootstrap_node.js:147:9)
    at bootstrap_node.js:538:3

also https://es6console.com/j2uho344/ this might be helpful.

i saw that Array(3,4).forEach.. works fine.

is that a bug? is that on purpose like that?

[addaleax]

is that on purpose like that?

It’s part of the language, yes. Your code is parsed as const a = 2[3,4].forEach(n => console.log(n)), which fails because 2 has no property 4 and so 2[3,4] returns undefined.

You can fix this by either using semicolons consistently, or add one whenever you start a line with an opening bracket or parenthesis.

[joyeecheung]

The question has been answered so I will go ahead and close this.