"strict mode": (not) everything you ever wanted to know about JavaScript's strict mode
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A 30-minute presentation given at Dealer.com on May 6, 2011. An overview of what "strict mode" means ECMAScript 5, and what it means (and does not mean) for everyday web development.
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"strict mode": (not) everything you ever wanted to know about JavaScript's strict mode
- 1. “strict mode” (Not) Everything You Ever Wanted to Know About JavaScript's Strict Mode
- 2. Just What is this so-called “strict mode”? What can it do for me? …or TO ME?
- 4. Quickly becoming an available option in major browsers
- 5. “A slight augmentation” of how ECMAScriptengines interpret/execute code
- 8. What about some concrete Examples?
- 9. "strict mode"; // and then the rest // but be careful when // concatenating! // "more compatible" way: (function(){ "use strict"; // and then the rest })(); How do I invoke it?
- 10. // "old" way foo = 'is now global'; "use strict"; bar = 'is not global'; // throws a ReferenceError Won’t let you do dumb things:implicit globals
- 11. // "old" way foo = { bar: function(){}, baz: 'name' }; with(foo){ bar(baz); } "use strict"; foo = { bar: function(){}, baz: 'name' }; with(foo){ bar(baz); } // ERROR! Won’t let you do dumb things:WITH(){}
- 12. …and other things you know better than to try and do in the first place. "use strict"; delete undeclaredVariable; // ERROR! var foo = { eval: function(val){} }; // ERROR! var arguments = somethingGlobal; // ERROR! varNaN = 'not a number'; // ERROR! var Infinity = (getAllNaturalNumbers() / 2); // ERROR! var undefined = 'undefined'; // ERROR!
- 13. // "old" way eval("that = 'this and that!';"); console.log('that is...:', that); "use strict"; eval("that = 'this and that!';"); console.log('that is...:', that); // ERROR! Not without controversy
- 14. // "old" way (function(){ console.log( 'this is...:', this ); })(); // this == window "use strict"; (function(){ console.log( 'this is...:', this ); })(); // this == undefined Not without controversy
- 15. Not without controversy "use strict"; function factorial(num){ if (num <= 1) { return 1; } else { return num * arguments.callee(num-1); } } // ERROR!
- 16. What does it mean for me?
- 17. What does it mean for me? (probably nothing)
- 21. Angus Croll: “JavaScript Strict Mode”
- 23. MDC: ECMAScript 5 support in Mozilla
- 25. Douglas Crockford: “Strict Mode is Coming to Town”
Notas do Editor
- ( Firefox has had it for quite some time… Chrome and Safari have it now… IE9? )
- Invoked as either- The first line in a whole JS file –or-- As the first line in a function
- Enforcing some rules that were common sense… and/or were not exactly built-in but should have been……and/but then we get to the controversy? (who in here has seen 'undefined' get defined as such for the sake of old IE versions?)
- But this isn't much of a controversy? - - restrictions on eval() are a blessing
- But this might get some hackles up… There's that whole bit about `this` being "broken" in JavaScriptBut if you're expecting `this` to scope up to `window`… now you have broken code
- Firefox 4 will complain:'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions or the arguments objects for calls to them
- it's opt-in – so you'd have to decide to use itAnd anyway it's just enforcing certain coding styles that you ought to be doing anywayAnd/but you're already linting right?And/but there is an argument to be made for NOT using it