2017 — 2021 update Since 2009 when this question was asked, JavaScript has evolved significantly. All other answers are now obsolete or overly complicated. Here is the current best practice: function sleep(ms) { return new Promise(resolve => setTimeout(resolve, ms)); } Or as a one-liner: await new Promise(r => setTimeout(r, 2000)); Or const sleep = ms … Read more
The difference is that apply lets you invoke the function with arguments as an array; call requires the parameters be listed explicitly. A useful mnemonic is “A for array and C for comma.” See MDN’s documentation on apply and call. Pseudo syntax: theFunction.apply(valueForThis, arrayOfArgs) theFunction.call(valueForThis, arg1, arg2, …) There is also, as of ES6, the … Read more
You can use the for-in loop as shown by others. However, you also have to make sure that the key you get is an actual property of an object, and doesn’t come from the prototype. Here is the snippet: var p = { “p1”: “value1”, “p2”: “value2”, “p3”: “value3” }; for (var key in p) … Read more
2022 update There’s a new JS standard called structured cloning. It works on all browsers: const clone = structuredClone(object); Old answer To do this for any object in JavaScript will not be simple or straightforward. You will run into the problem of erroneously picking up attributes from the object’s prototype that should be left in … Read more
Empty string, undefined, null, … To check for a truthy value: if (strValue) { // strValue was non-empty string, true, 42, Infinity, [], … } To check for a falsy value: if (!strValue) { // strValue was empty string, false, 0, null, undefined, … } Empty string (only!) To check for exactly an empty string, … Read more
Use Math.round() : Math.round(num * 100) / 100 Or to be more specific and to ensure things like 1.005 round correctly, use Number.EPSILON : Math.round((num + Number.EPSILON) * 100) / 100
It’s easy enough to write your own comparison function: function compare( a, b ) { if ( a.last_nom < b.last_nom ){ return -1; } if ( a.last_nom > b.last_nom ){ return 1; } return 0; } objs.sort( compare ); Or inline (c/o Marco Demaio): objs.sort((a,b) => (a.last_nom > b.last_nom) ? 1 : ((b.last_nom > a.last_nom) … Read more
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; console.log(obj[“key”] !== undefined); // false, but the key exists! You should instead use the in operator: var obj = { key: undefined }; … Read more
Three main options: for (var i = 0; i < xs.length; i++) { console.log(xs[i]); } xs.forEach((x, i) => console.log(x)); for (const x of xs) { console.log(x); } Detailed examples are below. 1. Sequential for loop: var myStringArray = [“Hello”,”World”]; var arrayLength = myStringArray.length; for (var i = 0; i < arrayLength; i++) { console.log(myStringArray[i]); //Do … Read more
You want the splice function on the native array object. arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it’s just an insert). In this example we will create an array and add an element to it into index 2: var arr = []; arr[0] = … Read more