javascript - Assign the obtained text element to var x; why can't it be judged whether the input text is empty?

Assign the obtained text element to var x; why does it not take effect to determine whether the input text is empty? document.getElementById("demo").innerHTML; Is the element obtained a string or something else? It is a string. Why does using x.length to determine the length of a string no...

我想大声告诉你 2017-05-18 11:00:49 0  4  524

Python determines whether a variable exists

How to determine if a variable exists in Python? {Code...} This way, you can make a judgment before making a decision and report an error.

阿神 2017-07-05 10:35:30 0  1  1149

javascript - [Quickly determine if the array is empty] []==false Why does it return true?

{Code...} It can be seen that this can quickly determine whether the array is empty, but there are some doubts in principle. Known: 1. Equality operator "==": convert first and then compare. If one of the operands is a boolean, it is converted to a numeric value before comparing for equali...

習慣沉默 2017-07-05 10:51:52 0  6  1270

javascript - How to determine whether the value of src is empty?

{Code...} The src of img is read from the background, and the img is hidden when no image is uploaded in the background. But in the case of src=" ", the content of the value is the path of the current web page. How to change this judgment?

ringa_lee 2017-07-05 10:51:08 0  2  973

javascript - How to determine the drawn graphics under CANVAS

How do I judge what I am drawing on the canvas? For example, I use lines to draw a heart or a V. . How to determine whether it is heart or V? . And judge the similarity between two people's paintings. The condition can be one stroke, not multiple strokes

PHP中文网 2017-05-16 13:27:54 0  2  631

How to determine if composer is installed successfully?

How to determine if composer is installed successfully?

我爱Java 2018-02-19 13:32:39 0  3  1703

javascript - Determine user network environment

Please tell me how to use js to determine whether the user's network is useful? That is, I want to determine whether the user can use the external network? And make sure he has access to the Internet? God, please help me. . .

阿神 2017-07-05 11:07:13 0  3  1111

It is determined that line 10 has a </tr> end tag. If it is determined that line 20 has no </tr> tag, then why is there no </tr> tag?

Determine that line 10 has a </tr> end tag. Determine that line 20 has no </tr> tag.

黄小川 2018-10-19 09:14:43 0  1  1320

javascript - In addition to judging UA, is there any other way to judge whether the request comes from mobile or PC?

UA is too easy to be forged. I would like to ask if there are other methods that are not easy to forge to determine whether the request comes from PC or mobile. I temporarily want to (check) a way to determine whether it is triggered based on the window.ontouchstart method, but it seems to be easy. ...

ringa_lee 2017-05-18 10:59:01 0  3  566

Java uses the simplest if to determine whether the date is early or late

The date consists of three int data, namely year, month, day. You cannot use any function, just use the simplest if to judge. Does anyone have any simple method? Conventional: If is nested inside if, if year is equal, judge month, and then judge day directly as year1000000+month100+day. One if can b...

给我你的怀抱 2017-05-17 10:08:33 0  2  681

vue.js - Can javascript determine whether a file exists? ? ?

I want to know if javascript can determine whether a file exists based on its address path? I made a vue dynamic menu. I want to check whether the component component file exists. If it does not exist, I will continue to go out without pushing the route. Is there any way to tell...

为情所困 2017-05-19 10:42:38 0  5  1726

php - About a judgment condition written in the background

//Liver function function is_gangongneng(){ {code...}} This automatically determines whether it is abnormal. If you want to write the judgment conditions in the background and let the customer define the judgment conditions in the background, what should you do?

習慣沉默 2017-06-16 09:18:54 0  1  698

javascript - Node's process.platform determines the number of computer digits

Is the number of digits determined by node wrong?

阿神 2017-06-12 09:22:21 0  1  642

javascript - Ask for advice on jQuery judgment logic?

How to determine if the checkboxes under all other sibling elements of the clicked tr are checked? Please give me some advice!!!

阿神 2017-05-19 10:15:03 0  3  497

How to write this judgment formula?

$ Myrank = 1 to 10 No Price = 100 Judging $ Myrank Value like $ Myrank

小贾 2018-06-20 12:57:10 0  0  794

linux - How to determine the distribution version in shell script?

How to determine which distribution is in a shell script?

PHP中文网 2017-06-19 09:07:26 0  1  1189

javascript - How to determine whether the DOM element is loaded? Including dynamically added with JS

domcontentloaded can determine whether the page DOM is loaded, but it cannot determine whether it is dynamically added. How to determine this?

淡淡烟草味 2017-05-19 10:10:59 0  2  485

javascript - js determines whether the user's network can access the Internet?

How does the front end determine whether the user's network can access the Internet? Because some users cannot have an internal network without an external network, so if they want to detect those who cannot access the Internet, they can cancel the connection to the external link. Can anyone with ex...

女神的闺蜜爱上我 2017-07-05 10:51:37 0  9  1023

How to determine $func in $func($arr) as an anonymous function

How to determine $func in $func($arr) as an anonymous function

江湖再见 2023-05-05 21:28:00 0  0  540

javascript - js determines whether there are duplicate values ​​in the value in the JSON object?

How to judge if the value of specDesc in JSON object cannot be the same

给我你的怀抱 2017-06-12 09:32:44 0  4  1145