如何使用正则表达式根据 javascript 中的条件从字符串开头删除 substring？

Question

I have a string like this

term = "Hey there how you doing?"

Now because of some issues in the API, I sometimes receive undefined in the beginning of the string.

term = "#0undefinedHey there how you doing?"

OR

term = "#1undefined Hey there how you doing?"

Now I can check the presence of undefined in the beginning of the sentence by doing something like

if(term.indexOf("undefined") == 0) {
    //processing logic
}

But as you can see there is a presence of #n with the undefined where n can be any single digit number.

I want a regex solution such that it ignores #n and looks for undefined in the beginning of the sentence and remove the #n and undefined .

So the final string if undefined is present will be

term = "Hey there how you doing?" // removed #nundefined

How can I do this with regex?

Answer 1

 let s = "#0undefined Hello World;". console.log(s,replace(/^\#[0-9]*undefined\s*/;'')); const regex = RegExp('^\#[0-9]*undefined'). console.log('Has undefined = ' + regex;test(s));

Answer 2

If this number next to undefined makes any sense to you, you can try:

 const matches = "#1undefined Hey there how you doing?".match(/#([0-9]*)undefined?(.*)/); console.log(matches);

This will give you the number under matches[1] while your cleaned message will be at matches[2] .

---

If you just care about the message, you can use .replace as another user suggested to clean your output:

 const output = "#1undefinedHey there how you doing?".replace(/#([0-9]*)undefined?/, ''); console.log(output);