Implement default parameters for NodeJS

[apastuhov]

TypeScript Version: 1.8.10
NodeJS LTS Version: 4.4.7

I have a project, which I write for NodeJS. I use async/await so there is need to set tartget: es6. But when I wrote function(or lamba) with default parameter value, compiler work well, but NodeJS gave me an error.

TSConfig

{
    "compilerOptions": {
        "target": "es6",
        "module": "commonjs"
    }
}

Code

function foo(bar = 1) {
    console.log(bar);
}
foo();

Expected behavior:

Output JS:

function foo(bar) {
    if (bar === void 0) { bar = 1; }
    console.log(bar);
}
foo();

Display 1 as output.

Actual behavior:

Output JS:

function foo(bar = 1) {
    console.log(bar);
}
foo();

Run this code with NodeJS (v5.7.0) and get the error:

function foo(bar = 1) {
                          ^

SyntaxError: Unexpected token =
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:387:25)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at startup (node.js:141:18)
    at node.js:933:3

Assumption:

It would be great to set default parameters values via if for NodeJS, in case that problem occurs on NodeJS LTS.

[vladima]

Default parameters in node are available under a flag --harmony-default-parameters and eventually should be enabled by default.

[DanielRosenwasser]

I'll point out that we have #4692 which covers granular targeting for certain feature sets, so I'm going to close in favor of that.