Python String.startswith() with a list of strings in Javascript

Question

Python startswith() allows me to test if a string starts with a tuple of strings as shown below, which is what I want to achieve with JavaScript:

testvar = 'he', 'hi', 'no', 'ye'
if my_string.startswith(testvar):
    return True

I have seen this SO question and it did not completely help in achieving this.

I need to have a JavaScript code that will do the same thing with the Python code above.

Can't you use the answers from the other question by using a loop? — shuttle87, Jul 29 '15 at 14:18
See this question http://stackoverflow.com/questions/646628/how-to-check-if-a-string-startswith-another-string — Mazdak, Jul 29 '15 at 14:19

dreamingblackcat · Answer 1 · 2015-07-29T15:44:04.583

Since there has been many solutions for having an array passed as argument, I am gonna post a solution splat "*" style arguments:

String.prototype.startsWithSplat = function(){ 
  var args = Array.prototype.slice.call(arguments, 0, arguments.length); 
  var i;
  var matched = false;
  var self = this;
  for(i = 0; i < args.length; i++){
    if(self.slice(0, args[i].length) == args[i]){
      matched = true;
      break;
    }
  }
  return matched;
}

Then you can just call:

my_string.startswith('he', 'hi', 'no', 'ye');

Paul S. · Accepted Answer · 2015-07-29T14:27:40.210

All you need is a simple loop over an Array with one of the answers shown there,

var testvar = ['he', 'hi', 'no', 'ye'];

function startsWith2(haystack, needles) {
    var i = needles.length;
    while (i-- > 0)
        if (haystack.lastIndexOf(needles[i], 0) === 0)
            return true;
    return false;
}

startsWith2('hello world', testvar); // true
startsWith2('foo bar baz', testvar); // false

Similarly for endsWith;

function endsWith2(haystack, needles) {
    var i = needles.length, j, k = haystack.length;
    while (i-- > 0) {
        j = k - needles[i].length;
        if (j >= 0 && haystack.indexOf(needles[i], j) === j)
            return true;
    }
    return false;
}

score 0 · Answer 3 · answered Jul 29 '15 at 14:20

Since they're all the same length you could just do:

testvar = ['he', 'hi', 'no', 'ye']
return testvar.indexOf(my_string.substring(0,2)) > -1

And some examples:

// Examples:
testvar = ['he', 'hi', 'no', 'ye']
my_string = 'hello'
testvar.indexOf(my_string.substring(0,2)) > -1
true

my_string = 'apples'
testvar.indexOf(my_string.substring(0,2)) > -1
false

score 0 · Answer 4 · answered Jul 29 '15 at 14:21

You can run a reduce operation over your array of tests to find if a variable starts with any of them.

var testVar = ['he', 'hi', 'no', 'ye'];
var myString = 'hello';

var startsWithAny = testVar.reduce(function (returnValue, currentTest) {
  return returnValue || myString.startsWith(currentTest);
});

if (startsWithAny) {
  return true;
}

score 0 · Answer 5 · answered Jul 29 '15 at 14:25

0

var testvar = ['he','hi','no','ye'];
var str = "hello";

for(i = 0; i < testvar.length; i++)
{
   if (str.startsWith(testvar[i]) == true)
            console.log(str+" starts with: "+testvar[i]);
}

answered Jul 29 '15 at 14:25

FirebladeDan

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Python String.startswith() with a list of strings in Javascript

5 Answers5