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In JavaScript, what does “assert” mean?


In JavaScript, what does assert mean?

I’ve seen something similar like this:

assert(function1() && function2() && function3(), "some text");

And I’m curious about the assert() method’s purpose.

Asked by frrlod

Solution #1

In JavaScript, there is no standard assert. Perhaps you’re using a library that supplies one; for example, if you’re using Node.js, the assertion module may be used. (Console.assert is provided by browsers and other environments that provide a console that implements the Console API.)

The most common use of an assert function is to throw an error if the expression provided into it is false; this is part of the assertion checking idea. Assertions (as they’re known) are often used exclusively in “testing” or “debug” builds, and are removed from production code.

Assume you have a function that was designed to accept a string at all times. You’d want to know if someone used something other than a string to call that function (without having a type checking layer like TypeScript or Flow). So here’s what you could do:

assert(typeof argumentName === "string");

If the condition was untrue, assert would throw an error.

A very basic version might be as follows:

function assert(condition, message) {
    if (!condition) {
        throw message || "Assertion failed";

Better still, utilise the Error object, which has the benefit of collecting stack traces and other useful information:

function assert(condition, message) {
    if (!condition) {
        throw new Error(message || "Assertion failed");

Answered by T.J. Crowder

Solution #2

You can use console.assert if you’re using a recent browser or nodejs (expression, object).

For more information:

Answered by joaoprib

Solution #3

The other responses are correct: there isn’t an assert function built into ECMAScript5 (as opposed to JavaScript, which works almost everywhere), but certain browsers provide it or have add-ons that do. While it’s usually ideal to use a well-known / popular / well-maintained library for this, a “poor man’s assert” function for academic purposes would look like this:

const assert = function(condition, message) {
    if (!condition)
        throw Error('Assert failed: ' + (message || ''));

assert(1 === 1); // Executes without problem
assert(false, 'Expected true');
// Yields 'Error: Assert failed: Expected true' in console

Answered by jacobq

Solution #4

assert() is a javascript function that isn’t native to the language. It’s a one-of-a-kind feature created by someone. You’ll have to look for it on your page or in your files and upload it so that anyone can figure out what it’s up to.

Answered by Crayon Violent

Solution #5

check this:

It’s for putting JavaScript to the test. Despite the fact that this code is only five or six lines long, it gives you a lot of power and control over your code when testing.

The assert function takes two inputs:

outcome: A boolean value that indicates whether your test was successful or unsuccessful.

description: A brief summary of your test.

The assert method then produces a list item, assigns it a class of “pass” or “fail” depending on whether your test returned true or false, and appends the description to it. Finally, the coded block is placed on the page. It’s really basic, yet it works flawlessly.

Answered by Amrendra

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