What to say about null and false values in javaScript
JavaScript is the most popular programming language in the world. There are five types of empty values and false values in javaScript, namely false, null, undefined, "", and 0. Broadly speaking, these five values are invalid or null values of the corresponding data types
JavaScript is the most popular programming language in the world. This language can be used in HTML and the web, and can be used on a wide range of devices such as servers, PCs, laptops, tablets, and smartphones.
JavaScript is a scripting language
JavaScript is a lightweight programming language.
JavaScript is programming code that can be inserted into HTML pages.
JavaScript, when inserted into an HTML page, can be executed by all modern browsers.
JavaScript is easy to learn.
There are five types of null and false values in javaScript, namely false, null, undefined, "", and 0. In a broad sense, these five values are invalid or null values of the corresponding data type.
What these five values have in common is that the false branch will be executed when the if statement is executed, and the true branch will be executed when the corresponding non-statement is executed.
1 undefined
In javaScript, undefined is derived from null, and the browser default variable is undefined when the variable is initialized. Code example:
var str; alert(str);//undefined
Also
if(undefined == null) { alert("undefined == null 为true"); }
Popup: undefined == null is true
2 null
null represents a non-existent object, code example:
var obj = document.getElementById("btn"); alert(obj);//null
Although the type of null is object, null does not have the characteristics of an object. We cannot perform default calls of object instances such as null.toString(), null.constructor, etc.
The execution result of null ==undefined is true. In addition, assign the variable to null to facilitate garbage collection.
3 "",0,false
"",0,false appear as false values in the if statement, but they are all meaningful data and are just used as null values or False value.
"".toString(),(0).toString(), false.toString() are all legal executable statements.
In addition
if(0 == []){ alert("0 ==[] 为true"); } if(0 == ''){ alert("0 =='' 为true"); } if(0 ==false){ alert("0 ==false 为true"); }
The browser pops up in turn:
0 ==[] 为true 0 =='' 为true 0 ==false 为true if("" == false){ alert(‘“”== false 为true'); }
The browser pops up:
""== false is true
js Five types of null values:
typeof(undefined) == 'undefined' typeof(null) == 'object' typeof("") == 'String' typeof(0) == 'number' typeof(false) == 'boolean'
The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.
Related articles:
How to implement the web version of the calculator in JS
How to implement the parabolic trajectory of the ball using JS
How to implement binary tree traversal using JavaScript
How to implement cookie cross-domain in axios
The above is the detailed content of What to say about null and false values in javaScript. For more information, please follow other related articles on the PHP Chinese website!

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