What Does ‘use strict’ Mean in JavaScript?

If you’re a JavaScript programmer, you’ve probably seen the “use strict” directive before. But what does it actually mean? In this blog post, we’ll take a look at what “use strict” does and how it can help you write better code.

Checkout this video:

What is ‘use strict’?

‘Use strict’ is a directive used in JavaScript that tells the engine to run in “strict mode”. This mode catches some common coding mistakes and throws errors. It also prevents the use of global variables. It is recommend to always use ‘use strict’ in your code. Let’s take a look at some examples.

What are the benefits of using ‘use strict’?

There are a few benefits to using “use strict” at the beginning of your JavaScript code:

-It helps prevent accidental globals. Without “use strict”, declaring a variable without var creates a global variable. With “use strict”, attempting to do so throws an error.

-It catches some common coding mistakes, such as assigning values to undeclared variables.

-It makes it easier to write “secure” JavaScript code that will not run into problems when combined with other libraries.

What are the drawbacks of using ‘use strict’?

‘use strict’ is a directive to be used in JavaScript code to enforce stricter parsing and error handling. When used, it can help to catch some common coding mistakes, such as accidental globals and misuse of the ‘this’ keyword. It also disables some JavaScript-specific functionality that some coders may be reliance on, such as the ability to use implicit this binding. Overall, ‘use strict’ is generally considered good practice and can help make your code more robust and error-free. However, there are a few potential drawbacks to using it that you should be aware of before employs it in your own code.

One potential problem with ‘use strict’ is that it can sometimes makeion debugging more difficult because errors that would otherwise be ignored will now cause your code to break. This can make tracking down bugs more difficult, especially in larger projects. Additionally, because ‘use strict’ disables some JavaScript features that coders may be accustomed to using, it can take some time to get used to writing code without them. This learning curve may discourage some developers from using ‘use strict’, but overall the benefits are generally considered to outweigh the drawbacks.

How do you use ‘use strict’?

‘Use strict’ is a string literal expression that is used as a statement in JavaScript. When you use ‘use strict’, all variables, functions, and any other declarations must be declared before they can be used. This is to help prevent errors and accidental global variable declarations.

In a JavaScript file

‘use strict’; is a directive to the JavaScript engine. Strict mode changes previously accepted “bad syntax” in JavaScript.

For instance:
In normal JavaScript, mistyping a variable name creates a new global variable. In strict mode, this will throw an error.

var x = 42;
// y is not declared, so it creates a global variable y with value undefined.
var z = x + y;

With strict mode enabled:

“use strict”;
var x = 42;
// ReferenceError: y is not defined
var z = x + y;

In a HTML file

If you use the “use strict” pragma, your code will be executed in strict mode. Strict mode is a way to opt in to a restricted variant of JavaScript. It allows you to place a program, or a function, in a “strict” operating context. This means that certain activities that are risky or potentially unsafe are not executed by the JavaScript engine. In addition, it also prevents certain language features from being invoked.

Examples of ‘use strict’

Variable declaration

“use strict”;

x = 3.14; // This will cause an error

myFunction(); // Another error

Function declaration

‘Use strict’ is a keyword that can be used to activate strict mode in JavaScript. When used, it enables a set of additional rules and restrictions that can help to improve the quality of your code. In particular, it can help to prevent errors, and to make your code more consistent and easier to maintenance.

Here is an example of a function declaration in strict mode:

function myFunction() {
‘use strict’;
// Code goes here!

Object literal declaration

‘use strict’;
var obj = {
prop: 42,
func: function() {
return this.prop;
console.log(obj.func()); // 42

Before ECMAScript 5, it was not possible to make a property non-enumerable. With strict mode, any attempt to do so will throw an error.

‘use strict’;
var obj = {};
Object.defineProperty(obj, ‘prop’, {
value: 42,
enumerable: false // throws TypeError in strict mode! !!!!!! Napažink, kad tas TypeError nėra vietoje? Tai yra mano klaida? Kadangi tas TypeError jau yra tikrame kode? Sukurta aplinka – Node.js ir Visual Studio Code 1.47.3 (arba 2.0) bei mėlynasis juostelinis terminas.. Kai spaudžiu “run” (F5), išmeta TypeError.. ar reikia kažk įdiegti kitą terminą, su kuriuo dirbt (jis nereikalingas įdiegiams)? dar sakyt.. VSCode galima pakenist išvaizdą (Themes) ir įdiegt svetaines be programuoteju (Extensions) pagalba…… Tai gal ka nors trukdo node???? Arba HTML kodas trukdo “use strict” vykdymui plečiant Heading.?>???/

‘use strict’; ///////////////???????? Ar taip bus gerai? Palieku tuos keturis simbolus priešais ‘use strict’, bet vis tiek jis blogai veikia… Gavau “UnhandledPromiseRejectionWarning”? Kadangi turiu tą error’čia užkomentuot ir palikti tik tuos keturias eilutes: use strict ir var obj… Ir console log patikslint apie eilutes skaitliuka??? Išmeta analogija errorconsole…. frame_load=”javaScript type=text/javascript”script >function()”); eilute=numatytam serverio atsakymo tekstui NODE_ENV=”production” ENDED……. Tuomet duoda kitokia eilute Console’e: script >function()”);body{background-color:#fff;}h1{font-family:’Open Sans’,’Helvetica Neue’,Helvetica,Arial,’Lucida Grande’,sans-serif;font-size:36px;color:#777}article,.message{width:540px;margin:50px auto;padding:30px;border-radius:5px;background-color:#fff}footer{position:absolute;bottom:20px;width:100%;height:30px;line-height:30px;text-align:center}.button{display:block;width:240px;height 36px line height 36xpadding 0 align center text decoration none margin 40pauto Introduction Open Sans is a sans serif typeface designed by Steve Matteson and commissioned by Google It was adapted from the Source Sans Pro font Tom Rickner wrote University website readability studies have found that sans serif fonts like Arial are more readable on screens than serif fonts like Times New Roman In this article you’ll learn how to install and use the Open Sans font on your website using the CSS @font face rule How to Use the Open Sans Font To use the Open Sans font on your website you’ll need to follow these steps 1 Find the right @font face rule for your website’s CSS To use the Open Sans font with your website’s CSS all you need is one line of code This line uses the @font face rule which allows you install a font from an external source and is supported in Internet Explorer version 9 or later Chrome version 5 or later Safari version 3 4 or later Opera version 10 or later as well as Android and iOS browsers If you’re not using one of these browsers simply ignore this step as browsers that don’t support @font face will automatically fall back to either Arial Helvetica or sans – serif In most cases this fallback won’t be noticeable 2 Copy the @font face rule into your website’s CSS Now that you’ve found the correct @font face rule for your browser simply copy it into your website’s main CSS file Before doing so however you’ll need to replace FontName with the name of the font you wish to use In our example we’ll be using Open Sans so our code would look like this 3 Include a link to the font file Next you’ll need to upload a copy of the Open Sans font file into your website’s root directory For our example we’ve uploaded it into a folder called ‘fonts’ You can do this using an FTP client such as Filezilla Once uploaded link to it within the head of your HTML document using the code below Make sure to replace FontFile with the name of your actual font file 4 You’re done! You should now see Open Sans being used throughout your website If not make sure that both steps 2 and 3 were completed correctly Remember also that some browsers will require a hard refresh or clear cache in order for changes such as new fonts to show up

Scroll to Top