lint: add use strict to use es5+

[coolaj86]

No description provided.

[markin-io]

@coolaj86 could you please explain the purpose of this change? Is something does not work without the "use strict"?

[coolaj86]

Is something does not work without the "use strict"?

If you don't "use strict" then the JavaScript runs in ES3 mode rather than ES5 mode, which means the possibility of silent errors, odd behaviors, code that breaks the JIT compiler and wreaks havoc on performance for seemingly no reason.

If you have a linter integrated into your editor (jshint, eslint, etc), it would most likely catch things like accidental global scope, accidental modification of global this, accidental assignment to undefined, accidental corruption of prototypes, accidental use or parseInt of octals, modification of properties of strings, etc.

The problem with not having "use strict";, especially if you're not using a linter that enforces the strict rules, is that you just don't know when something is wrong.

Ex: You forget a new in front of a constructor-ish function and it works for the singleton, all tests pass, but then becomes impossible to debug when you have two instances of the object in the real application, or two objects with some same properties at runtime, etc.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode

There's only upside, no downside, and it's required as part of the ES5 spec to run in ES5+ mode.