ecmascript-5

I am not asking if this is okay: Object.prototype.method = function(){}; This is deemed evil by pretty much everyone, considering it messes up for(var i in obj) . The Real Question Ignoring Incompetent browsers(browsers that don't support Object.defineProperty ) Potential for property collision or overriding Assuming you have some incredibly useful method, is this considered wrong/unethical? Object.defineProperty(Object.prototype, 'methodOnSteriods',{ value: function(){ /* Makes breakfast, solves world peace, takes out trash */ }, writable: true, configurable: true, enumerable: false }); If

I'm wondering what is the difference between let and const in ES6 . Both of them are block scoped, as the example in the following code: const PI = 3.14; console.log(PI); PI = 3; console.log(PI); const PI = 4; console.log(PI); var PI = 5; console.log(PI); In ES5 the output will be: 3.14 3.14 3.14 3.14 But in ES6 it will be: 3.14 3 4 5 I'm wondering why ES6 allows the change of const value, the question is why should we use 'const' now? we can use 'let' instead? Note : jsbin can be used for testing, choose JavaScript to run ES5 code and Traceur to run it with ES6 capabilities. What you're

I started using arrow functions after I felt doing manual function/object bindings and scope related issues are headache but very rencently I came to know that it’s better to use normal function(ES5) than arrow function(ES6). My understanding about these functions Normal function in React: Bind object/function manually in order to play with state or props inside the function and to avoid scope related issues Bind object/function always in constructor but not directly in render If you do it in constructor then Webpack creates new object/function in bundle.js file only once when your component

I have an object that could be any number of levels deep and could have any existing properties. For example: var obj = { db: { mongodb: { host: 'localhost' } } }; On that I would like to set (or overwrite) properties like so: set('db.mongodb.user', 'root'); // or: set('foo.bar', 'baz'); Where the property string can have any depth, and the value can be any type/thing. Objects and arrays as values don't need to be merged, should the property key already exist. Previous example would produce following object: var obj = { db: { mongodb: { host: 'localhost', user: 'root' } }, foo: { bar: baz } };

This question already has an answer here: What are the rules for JavaScript's automatic semicolon insertion (ASI)? 5 answers As you might know, ECMAscript tries to be smart and will automatically insert semicolons if you didn't write those explicitly. Simple example function foo() { var bar = 5 return bar } will still work as expected. But there are some caveats if you rely on that. If we re-write that function like so function foo() { var bar = 5 return { bar: bar } } ..that function would now return undefined because the interpreter would insert that semicolon right after the return