SyntaxError: Unexpected token : when using destructoids with default values

[guymguym]

This code:

$ cat a.js 
'use strict';

const object = { field: 1 };
const { field: value = 0 } = object;
console.log(value);

Works on node v6:

$ node -v 
v6.11.2

$ node a.js 
1

Fails on istanbul 0.4.5:

$ istanbul help
...
istanbul version:0.4.5

$ istanbul cover a.js 
No coverage information was collected, exit without writing coverage information a.js:9
__cov_txVrA0tc0SvRcxzSCmLkhg.s['1']++;const object={field:1};__cov_txVrA0tc0SvRcxzSCmLkhg.s['2']++;const {value=0:value=0}=object;__cov_txVrA0tc0SvRcxzSCmLkhg.s['3']++;console.log(value);
                                                                                                                 ^

SyntaxError: Unexpected token :
    at createScript (vm.js:56:10)
    at Object.runInThisContext (vm.js:97:10)
    at Module._compile (module.js:542:28)
    at Object.Module._extensions.(anonymous function) [as .js] (node_modules/istanbul/lib/hook.js:107:24)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Function.Module.runMain (module.js:604:10)
    at runFn (node_modules/istanbul/lib/command/common/run-with-cover.js:122:16)
    at node_modules/istanbul/lib/command/common/run-with-cover.js:251:17

Here is the instrumented code:

$ istanbul instrument a.js 
"use strict";
var __cov_txVrA0tc0SvRcxzSCmLkhg = (Function('return this'))();
if (!__cov_txVrA0tc0SvRcxzSCmLkhg.__coverage__) { __cov_txVrA0tc0SvRcxzSCmLkhg.__coverage__ = {}; }
__cov_txVrA0tc0SvRcxzSCmLkhg = __cov_txVrA0tc0SvRcxzSCmLkhg.__coverage__;
if (!(__cov_txVrA0tc0SvRcxzSCmLkhg['a.js'])) {
   __cov_txVrA0tc0SvRcxzSCmLkhg['a.js'] = {"path":"a.js","s":{"1":0,"2":0,"3":0},"b":{},"f":{},"fnMap":{},"statementMap":{"1":{"start":{"line":3,"column":0},"end":{"line":3,"column":28}},"2":{"start":{"line":4,"column":0},"end":{"line":4,"column":36}},"3":{"start":{"line":5,"column":0},"end":{"line":5,"column":19}}},"branchMap":{}};
}
__cov_txVrA0tc0SvRcxzSCmLkhg = __cov_txVrA0tc0SvRcxzSCmLkhg[a.js'];
__cov_txVrA0tc0SvRcxzSCmLkhg.s['1']++;const object={field:1};__cov_txVrA0tc0SvRcxzSCmLkhg.s['2']++;const {value=0:value=0}=object;__cov_txVrA0tc0SvRcxzSCmLkhg.s['3']++;console.log(value);

This statement was malformed:

const {value=0:value=0}=object;

[AngryPidgeon]

+1, just ran into this issue while updating our code coverage tool.

The syntax where you assign a default value inside destructuring of an object seems to trigger this. Not great, but to work around you'd have to instead of const { field: value = 0 } = object; do const {field : value} = object; value = value || 0;

[guymguym]

@AngryPidgeon You best upgrade to use https://github.com/istanbuljs/nyc instead of this deprecated repo. It has not been active for 2 years now (see comment in readme)

[AngryPidgeon]

@guymguym thanks, I'll look into that. (I did get Istanbul working fine, but better to be update)