No, there is no built-in property that tells you how many properties the object has (which is what you’re looking for). The closest I can think of are two ES5 and higher features, Object.keys (spec | MDN) and Object.getOwnPropertyNames (spec | MDN). For instance, you could use Object.keys like this: console.log(Object.keys(quesArr).length); // “3” Object.keys returns … Read more
It’s called the module pattern http://toddmotto.com/mastering-the-module-pattern/ The main reason is for you to create truly private methods and variables. In your case, it’s not meaningful because it’s not hiding any implementation details. Here’s an example where it makes sense to use the module pattern. var MyNameSpace = {}; (function(ns){ // The value variable is hidden … Read more
What is an applicable example of using Maps over objects? I think you’ve given one good example already: You at least need to use Maps when you are using objects (including Function objects) as keys. in particular, “when would keys be unknown until runtime?” Whenever they are not known at compile time. In short, you … Read more
var keys = [‘foo’, ‘bar’, ‘baz’]; var values = [11, 22, 33] var result = {}; keys.forEach((key, i) => result[key] = values[i]); console.log(result); Alternatively, you can use Object.assign result = Object.assign(…keys.map((k, i) => ({[k]: values[i]}))) or the object spread syntax (ES2018): result = keys.reduce((o, k, i) => ({…o, [k]: values[i]}), {}) or Object.fromEntries (ES2019): Object.fromEntries(keys.map((_, … Read more
This behavior is useful for doing something like optional spreading: function foo(options) { const bar = { baz: 1, …(options && options.bar) // options and bar can be undefined } } And it gets even better with optional chaining, which is in Stage 4 now (and already available in TypeScript 3.7+): function foo(options) { const … Read more
Unless the variable k is defined, that’s probably what’s causing your trouble. Something like this will do what you want: var new_tweets = { }; new_tweets.k = { }; new_tweets.k.tweet_id = 98745521; new_tweets.k.user_id = 54875; new_tweets.k.data = { }; new_tweets.k.data.in_reply_to_screen_name=”other_user”; new_tweets.k.data.text=”tweet text”; // Will create the JSON string you’re looking for. var json = JSON.stringify(new_tweets); … Read more
I have researched this a bit. MDN is silent on the issue, and so is the spec (ES5, ES6). They only state that the property accessor must be a string, without any qualifications – in other words, there is no limit as far as the spec is concerned. That’s hardly surprising. How browsers handle it, … Read more
Both terms are defined in the ECMAScript specification: native object object in an ECMAScript implementation whose semantics are fully defined by this specification rather than by the host environment. NOTE Standard native objects are defined in this specification. Some native objects are built-in; others may be constructed during the course of execution of an ECMAScript … Read more
Virtually everything in javascript is an object, so you can “abuse” an Array object by setting arbitrary properties on it. This should be considered harmful though. Arrays are for numerically indexed data – for non-numeric keys, use an Object. Here’s a more concrete example why non-numeric keys don’t “fit” an Array: var myArray = Array(); … Read more
Use Array.prototype.sort(), eg myArray.sort((a, b) => a.distance – b.distance) The sort() method accepts a comparator function. This function accepts two arguments (both presumably of the same type) and it’s job is to determine which of the two comes first. It does this by returning an integer Negative (less-than zero): The first argument comes first Positive … Read more