JS substr and substring

I don't know why, every time I need to use a function that intercepts a string, I always tell the difference between substr and substring . But then again, these two really look alike. Why does JS have these two so "seemingly" things?

SUBSTR (start, [length])

Intercepts a string of length from the specified subscript start.

If start is negative, the count starts at the end of the string, such as 1, which starts at the bottom of the countdown. If the absolute value of this negative number is greater than the string length, then it is considered to be 0.

If length is 0 or negative, an empty string is returned, and if length is omitted, it is truncated from start to end.

SUBSTRING (start, [stop])

Intercepts a string from the subscript start to the stop (character that does not include the stop position).

If stop is omitted, the end is truncated. Start and stop must be non-negative integers, that is, 0,1,2 ...

If start is greater than Stop,js, they are automatically swapped and then calculated.

If Start equals stop, an empty string is returned.

The basic rule is this, this is the grammatical category of things, very thin and cumbersome, but also bad distinction. The scenario in which you actually use SUBSTR may be the following.

• Take the first few words of a large paragraph of text to form a thumbnail message.
• Get the first and the end of private information such as ID cards, bank cards, phone numbers, and then assemble and then publicly display.

Substring may be like this:

• Gets the last paragraph of the URI
• Get email address @ The following paragraph

They are often used with indexOf.

For more details, refer to MDN

Https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr

Https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring

JS substr and substring