The assert keyword is used when debugging code. The assert keyword lets you test if a condition in your code returns True, if not, the program will raise an AssertionError. You can write a message to be written if the code returns False, check the example below.
An assertion is a statement in the Java programming language that enables you to test your assumptions about your program. For example, if you write a method that calculates the speed of a particle, you might assert that the calculated speed is less than the speed of light.
The assert. equal() method tests if two values are equal, using the == operator. If the two values are not equal, an assertion failure is being caused, and the program is terminated. To compare the values using the === operator, use the assert.
There is no standard assert
in JavaScript itself. Perhaps you're using some library that provides one; for instance, if you're using Node.js, perhaps you're using the assertion module. (Browsers and other environments that offer a console implementing the Console API provide console.assert
.)
The usual meaning of an assert
function is to throw an error if the expression passed into the function is false; this is part of the general concept of assertion checking. Usually assertions (as they're called) are used only in "testing" or "debug" builds and stripped out of production code.
Suppose you had a function that was supposed to always accept a string. You'd want to know if someone called that function with something that wasn't a string (without having a type checking layer like TypeScript or Flow). So you might do:
assert(typeof argumentName === "string");
...where assert
would throw an error if the condition were false.
A very simple version would look like this:
function assert(condition, message) {
if (!condition) {
throw message || "Assertion failed";
}
}
Better yet, make use of the Error
object, which has the advantage of collecting a stack trace and such:
function assert(condition, message) {
if (!condition) {
throw new Error(message || "Assertion failed");
}
}
If using a modern browser or nodejs, you can use console.assert(expression, object)
.
For more information:
The other answers are good: there isn't an assert function built into ECMAScript5 (e.g. JavaScript that works basically everywhere) but some browsers give it to you or have add-ons that provide that functionality. While it's probably best to use a well-established / popular / maintained library for this, for academic purposes a "poor man's assert" function might look something 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
assert()
is not a native javascript function. It is a custom function someone made. You will have to look for it on your page or in your files and post it for anybody to help determine what it's doing.
check this:http://net.tutsplus.com/tutorials/javascript-ajax/quick-tip-quick-and-easy-javascript-testing-with-assert/
it is for testing JavaScript. Amazingly, at barely five or six lines, this code provides a great level of power and control over your code, when testing.
The assert function accepts two parameters:
outcome: A boolean, which references whether your test passed or failed
description: A short description of your test.
The assert function then simply creates a list item, applies a class of either “pass” or “fail,” dependent upon whether your test returned true or false, and then appends the description to the list item. Finally, that block of coded is added to the page. It’s crazy simple, but works perfectly.
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