Javascript form validation-first introduction to regular expressions_javascript skills

Recommended reading: Javascript form validation length

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Javascript form validation - unveiling regular expressions

JavaScript can be used to validate these input data in HTML forms before the data is sent to the server.

Verification date

The format of the date is relatively special and cannot be verified based on its length alone

Common date format: first use two digits to represent the day, then use two digits to represent the month, and finally use four digits to represent the year, with the period separated by a slash.

MM/DD/YYYY

Blogger: How to design a code that verifies whether the date conforms to the format?

Let’s first look at the logic of validating the date format

Take out the value in the form field and use "/" to split the string into an array

Analyze the "month" substring to see if it has only two characters and both are numbers

Analyze the "day" substring to see if it has only two characters and both are numbers

Analyze the "year" substring to see if it has only four characters and are all numbers

If the above conditions are met, it is also necessary to determine whether the input data has only two slashes. If there are more than two slashes, the subsequent content should be ignored

Blogger: Don’t be afraid, Javascript is quite powerful. It provides developers with a powerful built-in tool - regular expressions

It is specifically used to match text patterns

It is like a policeman with bright eyes, always observing every move of the suspect, and once he breaks the law, he will catch the bad guy╮(╯▽╰)╭

Now let’s look at a small example

Match pattern=/^d{5}$/

The character after the equal sign is the following expression

The first slash and the last slash: "/" regular expressions are surrounded by slashes

The second character: "^" character must start with the specified pattern, numbers cannot be used

The third character: "d" represents a number

Fourth character: "{5}" The only number must be repeated 5 times

The fifth character: "$" The string ends with the specified pattern

Well, the editor will introduce you to this much about Javascript form validation - the first knowledge of regular expressions. The next section will unveil regular expressions for you. For more content, please pay attention to the Script House website!