我如何让 JavaScript 在字符之前获取子字符串？

Question

Let's say I have a paragraph that says 55+5. I want to have JavaScript return everything before the plus. Is this possible using substrings?

Answer 1

Do you mean substring instead of subscript? If so. Then yes.

var string = "55+5"; // Just a variable for your input.

function getBeforePlus(str){

    return str.substring(0, str.indexOf("+")); 
   /* This gets a substring from the beginning of the string 
      to the first index of the character "+".
   */

}

Otherwise, I recommend using the String.split() method.

You can use that like so.

var string = "55+5"; // Just a variable for your input.

function getBeforePlus(str){

    return str.split("+")[0]; 
    /* This splits the string into an array using the "+" 
       character as a delimiter.
       Then it gets the first element of the split string.
    */

}

Answer 2

Yes. Try the String.split method: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/split

split() returns an array of strings, split by the character you pass to it (in your case, the plus). Just use the first element of the array; it will have everything before the plus:

var string = "foo-bar-baz"
var splitstring = string.split('-')
//splitstring is a 3 element array with the elements 'foo', 'bar', and 'baz'

Answer 3

Use split and shift .

var str = '55+5';

var beforePlus = str.split('+').shift();

console.log(beforePlus);
// -> "55"