The difference between css == === ==

CSS is a style sheet language used to beautify and layout web pages. It, like HTML and JavaScript, is one of the three main technologies for building Web interfaces. Although CSS is just a programming language, it has capabilities that are crucial to web development. There are many operators in CSS, including ==, ===, and =. These operators look very similar, but what are the differences between them? This will be described in detail below.

First of all, == is an equality operator. When using == to compare two values, it will first try to type cast the two values ​​before comparing their values. For example:

var x = 1;
var y = "1";
console.log(x == y); // 输出true

In this example, we compare a number 1 and a string "1", but we use the == operator instead of the === operator. Since JavaScript supports implicit type conversion, when comparing 1 and "1", JavaScript converts the string into the number 1, so the comparison result is true. However, there are some cases where using the == operator may lead to incorrect results, for example:

console.log(false == "0"); // 输出true
console.log(null == undefined); // 输出true
console.log(0 == ""); // 输出true

In these cases, using the == operator may lead to unexpected results because JavaScript will treat different types values ​​were compared. Therefore, in actual development, it is recommended to use the === operator.

Secondly, === is a strict equality operator. Unlike ==, it does not perform type conversion and will only return true if the type and value of the two values ​​are equal. For example:

var x = 1;
var y = "1";
console.log(x === y); // 输出false

In this example, although the number 1 and the string "1" are equal in value, they are of different types, so the === operator returns false. When comparing values, using the === operator can avoid problems during type conversion, so in actual development, it is recommended to use the === operator.

Finally, = is the assignment operator, which is used to assign a value to a variable. For example:

var x = 1; // 将1赋值给变量x

Here, the = operator assigns the number 1 to the variable x. Note that assignment operators cannot be used to compare values ​​or variables.

To sum up, ==, === and = are three completely different operators. == is the equality operator, when doing a comparison it will first try to type cast the two values ​​before comparing their values. === is a strict equality operator. It does not perform type conversion and will return true only when the type and value of the two values ​​are equal. = is the assignment operator, which is used to assign a value to a variable. In actual development, it is recommended to use the === operator to avoid problems during value comparison.

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