The role of question marks in js

The question mark in JavaScript is used with the ternary conditional operator to select one value from two values ​​based on a condition. The syntax of the ternary condition operator is: condition ? value1 : value2, where condition is a Boolean expression, and value1 and value2 are the two values ​​to be selected.

The role of question mark in JavaScript

In JavaScript, the question mark "?" operator is a ternary conditional operation A part of a symbol that selects one of two values ​​based on a condition.

Syntax

condition ? value1 : value2

Where:

• condition is a Boolean expression.
• value1 is the return value when the condition is true.
• value2 is the return value when the condition is false.

Working Principle

The ternary conditional operator works as follows:

• First, calculate the condition ( condition).
• If the condition is true, then value1 is returned.
• If the condition is false, then value2 is returned.

Examples

Here are some examples of using the ternary conditional operator:

// 检查一个数字是否为偶数
let isEven = number % 2 === 0 ? true : false;

// 根据年龄确定是否可以喝酒
let canDrink = age >= 21 ? "可以喝酒" : "不可以喝酒";

// 设置默认值
let name = name || "John Doe";

Note

The ternary conditional operator is a short alternative to the if-else statement. However, it has the limitation that it can only return one of two values, whereas an if-else statement can return any number of values.

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