What does colon mean in js

The colon in JavaScript has six uses: 1. Assignment operator; 2. Conditional operator (ternary operator); 3. Label statement; 4. Object literal; 5. Extension operator ( ES6); 6. Type annotations (TypeScript).

The meaning of colon in JavaScript

In JavaScript, colon (:), as an operator, has multiple uses.

1. Assignment operator

The most common use of colon is as an assignment operator. It assigns the value of an expression to a variable. For example:

<code class="javascript">let x = 10;
x += 5; // 等效于 x = x + 5</code>

2. Conditional operator (ternary operator)

The colon is also used as a conditional operator, also known as the ternary operator. It returns one of two values ​​based on a conditional expression. The syntax is as follows:

<code class="javascript">条件 ? 值1 : 值2</code>

For example:

<code class="javascript">const isEven = n => (n % 2 === 0) ? true : false;</code>

3. Label statements

Colons can be used to add labels to statements. This allows jumping to the marked statement using the break or continue statement. For example:

<code class="javascript">myLabel:
while (condition) {
  // ...
}</code>

4. Object literal

In object literals, colons are used to specify keys and values. For example:

<code class="javascript">const person = {
  name: "John Doe",
  age: 30
};</code>

5. Spread operator (ES6)

In ES6, colon can be used with the spread operator (...) for expansion Array or object. For example:

<code class="javascript">const arr1 = [1, 2, 3];
const arr2 = [...arr1, 4, 5]; // [1, 2, 3, 4, 5]</code>

6. Type annotation (TypeScript)

In TypeScript, the colon is used to specify the type of a variable or function. For example:

<code class="typescript">let num: number = 10;</code>

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