Javascript exclamation mark after variable

The double javascript exclamation mark after variable mark!! It has a specific purpose and can be used in various scenarios to cast a value to a boolean true or false explicitly. In this article, we will explore what the double exclamation mark means in JavaScript and why it is used.

For more information, check out the TypeScript docs and GitHub repo. The exclamation mark! We will be using these terms interchangeably in this article. But what does this operator do? The non-null assertion operator tells the TypeScript compiler that a value typed as optional cannot be null or undefined.

Javascript exclamation mark after variable

In many scripting languages, developers use the exclamation mark as a not operator. But when working with TypeScript, the exclamation mark acts as a non-null assertion operator. This non-null assertion will remove null and undefined values. If we define a string-type variable as string null , it means that the variable holds a string or null value. But suppose we define a function that accepts only a string type as a parameter. In that case, the TypeScript compiler will reject our variable value since there is a possibility that it will have a null value. Refer to the following code:. However, if you use the non-null assertion operator, you can convey to the TypeScript compiler that the stringWord variable is never null or undefined. You deserve them too. The function will accept the parameter studentName.

The primary use of the exclamation point in TypeScript is as the "non-null assertion operator.

In TypeScript, the exclamation mark! This post explores their various use cases and provides insights into when and how to use them effectively. The exclamation mark serves as a non-null assertion operator, indicating to the TypeScript compiler that a value will not be null or undefined. It can be used in various scenarios to enhance type inference and streamline your code. The non-null assertion operator! This is particularly useful when you, as a developer, are confident that a certain value will always be present. You can place the exclamation mark immediately after a variable or property to assert its non-nullability.

For more information, check out the TypeScript docs and GitHub repo. The exclamation mark! We will be using these terms interchangeably in this article. But what does this operator do? The non-null assertion operator tells the TypeScript compiler that a value typed as optional cannot be null or undefined. For example, if we define a variable as possibly a string or undefined, the! In these cases, if we try to reference that variable as a definite type, then the TypeScript compiler would give us an error message, such as the following:.

Javascript exclamation mark after variable

The exclamation mark non-null assertion operator removes null and undefined from the type of an expression. It is used when we know that a variable that TypeScript thinks could be null or undefined actually isn't. The exclamation mark non-null assertion operator removes null and undefined from a type. The emp parameter in the function is marked as optional , which means that it can either be of type Employee or be undefined. Had we not used the non-null assertion operator, we would have gotten an error when trying to access the name property. The emp parameter is possibly undefined , so we cannot safely access a property on it, as it could potentially cause a runtime error. It's very important to note that the exclamation mark operator is simply a type assertion. It doesn't check if the specified variable is not null and not undefined. When we use the non-null assertion operator, we effectively tell TypeScript that this variable is never going to be null or undefined and not to worry about it.

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Consider whether a property should genuinely be optional before using a question mark. We can solve this issue by adding an exclamation mark after the studentName and making it a string type. Until the element is rendered, ref. For example, arg? A JavaScript variable can be instantiated with string and changed to object , null , or number during the execution of the code. Everything looks fine in the code but imagine if the type of the variable students can be undefined. Save my name, email, and website in this browser for the next time I comment. Share Share Share Share Share. I wrote a book in which I share everything I know about how to become a better, more efficient programmer. In such cases,! The non-null assertion can safely be used in this case since we can be certain we would not make it past validatePerson if person was undefined:. Overuse or misuse can undermine the very purpose of TypeScript, which is to catch errors at compile time rather than at runtime. It exemplifies TypeScript's flexible approach to typing, allowing developers to override the compiler's strictness when they have specific knowledge about the values in their code.

The logical NOT!

The alternative at the time was to write your assertions completely inline which can create messy, tangled code for complex type checks. You can use the question mark in conjunction with conditional type checks to handle scenarios where a property might be present or absent. Table of Contents 1. As we mentioned earlier, applying the!! What the postfix bang effectively says is "Hey, TypeScript even though you think this is a type error trust me it's not ". To make it easy for developers to include Syncfusion JavaScript controls in their projects, we have shared some working ones. Stay ahead of the curve. Refer to the following code:. If we define a string-type variable as string null , it means that the variable holds a string or null value. Optional chaining is a TypeScript shorthand that allows us easily handle the cases where the variable is defined or not. All Rights Reserved. This section covers essential best practices when using exclamation marks and question marks in TypeScript. It is used when we know that a variable that TypeScript thinks could be null or undefined actually isn't. However, in some cases, we have to disable the strict type checks. Twitter GitHub Linkedin.