如何在 JavaScript 中的“+”号之前选择一个整数

Question

I'm currently working on a calculator and for certain reasons (long story) I don't want to use the eval function.

so what I want to do is

var exp = document.form.textview.value; 
//everything on the calc is displayed in a form
var a = intiger up until the + sign

Now I have no idea how to do it, I tried doing

var a = exp.charAt(0)

but that just gives me the first character, what if the number is 2 digits.

all help is appreciated and thank you for reading have a nice day, larwa

Answer 1

So as i understand it you're trying to find all characters up to the + sign In the example of 12324+ you want to return 12324?

I would therefore use the "split" method on the string.

var value = "12324+";
var number = value.split('+')[0];

This will split the string into an array and return the first index (the number) to the number variable

Answer 2

Recognize an integer at the beginning of your input string:

JS' parseInt function does pretty much what you want, eg using your var names:

var a = parseInt(exp);

For a working example, see here:

 $(function(){ $('#inp').keyup(function(ev){ const val = $(ev.target).val(); // this is the important part: const int = parseInt(val); console.log(int); }) });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <input id="inp" /> <h3>value:</h3> <div id="out"> </div>

Recognize all integers in your input string

To get all occurrences of integers in your input string you may use

var a = exp.match(/-?\d+/g).map(s => parseInt(s))

which will return an array of all separate integers. Working example:

 $(function(){ $('#inp').keyup(function(ev){ const val = $(ev.target).val(); // this is the important part: const matches = val.match(/-?\\d+/g).map(s => parseInt(s)); console.log(matches); }) });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <input id="inp" /> <h3>value:</h3> <div id="out"> </div>