Understanding this “hack” requires understanding several things: Why we don’t just do Array(5).map(…) How Function.prototype.apply handles arguments How Array handles multiple arguments How the Number function handles arguments What Function.prototype.call does They’re rather advanced topics in javascript, so this will be more-than-rather long. We’ll start from the top. Buckle up! 1. Why not just Array(5).map? … Read more
It’s to avoid collisions – in general, issues with objects that do not have the property with the value that you expect. Objects in JS are often used as key-value-maps, and the keys can be arbitrary strings – for example __defineGetter__, hasOwnProperty or something less special. Now when you want to invoke such a function … Read more
Is the function created by Function constructor also a closure? Yes, it closes over the global scope. That might be unintuitive because all other JavaScript closures close over their lexical scope, but it still matches our definition of a closure. In your example, a is a free variable, and resolves to the a in an … Read more
You can’t break from a forEach. I can think of three ways to fake it, though. 1. The Ugly Way: pass a second argument to forEach to use as context, and store a boolean in there, then use an if. This looks awful. 2. The Controversial Way: surround the whole thing in a try-catch block … Read more
[] is an array. This array isn’t used at all. It’s being put on the page, because using an array gives you access to array prototypes, like .forEach. This is just faster than typing Array.prototype.forEach.call(…); Next, forEach is a function which takes a function as an input… [1,2,3].forEach(function (num) { console.log(num); }); …and for each … Read more
This function, using the arguments you specified, should add/update the data in the obj container. Note that you need to keep track of which elements in obj schema are containers and which are values (strings, ints, etc.) otherwise you will start throwing exceptions. obj = {}; // global object function set(path, value) { var schema … Read more
Use Object.keys: var foo = { ‘alpha’: ‘puffin’, ‘beta’: ‘beagle’ }; var keys = Object.keys(foo); console.log(keys) // [‘alpha’, ‘beta’] // (or maybe some other order, keys are unordered). This is an ES5 feature. This means it works in all modern browsers but will not work in legacy browsers. The ES5-shim has a implementation of Object.keys … Read more
If you’re in the global scope then there’s not much difference. Read Kangax’s answer for explanation If you’re in a function then var will create a local variable, “no var” will look up the scope chain until it finds the variable or hits the global scope (at which point it will create it): // These … Read more
If I am reading your question correctly, you want to time the fastest way to preform some kind of loop. There are a number of looping constructions in JavaScript that include: for while do… while recursion setTimeout/setInterval for…in for…of generators Of these, the basic for loop is generally the fastest as it has the least … Read more
You can match using unicode and replace the unicodes later Unicode finder let str = `«Name» has an account on the bank «Bank Name»` let final = str.match(/\u00AB.*?\u00BB/gu).map(v=>v.replace(/\u00AB|\u00BB/g,”)) console.log(final) Alternatively you can use exec and get the value from captured group let str = `«Name» has an account on the bank «Bank Name»` let final … Read more