CODEWITHSUNDEEP
javascript
Luca
Luca

Reputation: 20919

How to detect string which contains only spaces?

A string length which contains one space is always equal to 1:

alert('My str length: ' + str.length);

The space is a character, so:

str = "   ";
alert('My str length:' + str.length); // My str length: 3

How can I make a distinction between an empty string and a string which contains only spaces? How can I detect a string which contain only spaces?

Upvotes: 143

Views: 205397

Answers (10)

Ian Carter
Ian Carter

Reputation: 1043

Typecasting to Number can detect whitespace-only strings (if strings containing only zeros can be excluded):

if (+'   ' === 0) console.log('is whitespace');

however:

  • number-casting only wins obscurity
  • regex wins readability
  • trimed-length-duplicate-check wins brevity
  • fail-early-whitelist-loop function wins performance

 /**
* use a fail-early-whitelist-loop (avoiding regular-expressions or length checks on trimmed duplicates)
* using `charCodeAt(i)` (which is faster than `[index]`)
*/
const isOnlySpace = (s, emptyIsTrue=false) => {
    let i = String(s || '').length;
    if (i === 0) return emptyIsTrue;
    while (--i > -1) {
        switch (s.charCodeAt(i)) {
            case 0x0020: case 0x0009: case 0x000A: case 0x000B: case 0x000C: case 0x000D:
            case 0x0085: case 0x00A0: case 0x1680: case 0x180E: case 0x2000: case 0x2001:
            case 0x2002: case 0x2003: case 0x2004: case 0x2005: case 0x2006: case 0x2007:
            case 0x2008: case 0x2009: case 0x200A: case 0x2028: case 0x2029: case 0x202F:
            case 0x205F: case 0x3000:
            continue;
            default:
                return false;
        }
    }
    return true;
};

const tests = ['',' ', '\t\n\r','0',' 0 ','x',' 404 '];

console.log(tests.filter(isOnlySpace)); // fastest
console.log(tests.filter(x => String(x || '').trim().length === 0)); // fast
console.log(tests.filter(x => /^\s*$/.test(x))); // 33% slower
console.log(tests.filter(x => +x === 0 && String(x).indexOf('0') === -1)); // 40 % slower
console.log(tests.filter(x => Number('1 ' + x) === 1)); // 66% slower

Upvotes: 0

Rory McCrossan
Rory McCrossan

Reputation: 337560

To achieve this you can use a Regular Expression to remove all the whitespace in the string. If the length of the resulting string is 0, then you can be sure the original only contained whitespace. Here's a working example:

const isWhitespaceString = str => !str.replace(/\s/g, '').length

console.log('isWhitespaceString str1:', isWhitespaceString('  w ')); // false
console.log('isWhitespaceString str2:', isWhitespaceString('    ')); // true
console.log('isWhitespaceString str3:', isWhitespaceString('')); // true

Upvotes: 207

Mateen
Mateen

Reputation: 533

You can do this by simply using trim.

var str = "   ";
if (str.trim().length == 0)
{
   console.log("Your string contains only white spaces.")
   console.log(`Your string is >>${str}<<`);
}

Upvotes: 4

pmrotule
pmrotule

Reputation: 9692

The fastest solution would be using the regex prototype function test() and looking for any character that is not a space, tab, or line break \S:

var str1 = '  w ' // false
var str2 = '    ' // true
var str3 = '' // true

const isWhitespaceString = str => !/\S/.test(str)

console.log('isWhitespaceString str1', isWhitespaceString(str1))
console.log('isWhitespaceString str2', isWhitespaceString(str2))
console.log('isWhitespaceString str3', isWhitespaceString(str3))

In case you have a super long string, it can make a significant difference as it will stop processing as soon as it finds a non-space character.

Upvotes: 76

Sabir Hassan
Sabir Hassan

Reputation: 41

If we want to check if string contains only white spaces, then this might be helpful.

const str = '   ';
console.log(/^\s+$/.test(str));

This will log true.

Upvotes: 2

Unmitigated
Unmitigated

Reputation: 89149

if(!str.trim()){
  console.log('string is empty or only contains spaces');
}

String#trim() removes the whitespace at the start and end of the string. If the string contained only whitespace, it would be empty after trimming, and the empty string is falsey in JavaScript.

If the string might be null or undefined, we need to first check if the string itself is falsey before trimming.

if(!str || !str.trim()){
   //str is null, undefined, or contains only spaces
}

This can be simplified using the optional chaining operator.

if(!str?.trim()){
   //str is null, undefined, or contains only spaces
}

Upvotes: 45

Matthew Trent
Matthew Trent

Reputation: 3264

This works in Dart not Javascript. However, when I searched up how to do this with Dart this question came up, so I figured others may need the Dart answer.

String foo = '        ';
if (foo.replaceAll(' ', '').length == 0) {
print('ALL WHITE SPACE');
}
else {
print('NOT ALL WHITE SPACE');
}

To further clarify, the String ' d ' will print 'NOT ALL WHITE SPACE' and the String ' ' will print 'ALL WHITE SPACE'.

Upvotes: -1

bobbyg603
bobbyg603

Reputation: 3840

Similar to Rory's answer, with ECMA 5 you can now just call str.trim().length instead of using a regular expression. If the resulting value is 0 you know you have a string that contains only spaces.

if (!str.trim().length) {
  console.log('str is empty!');
}

You can read more about trim here.

Edit: After looking at this a few years later I noticed this could be simplified further. Since the result of trim will either be truthy or falsy you can also do the following:

if (!str.trim()) {
     console.log('str is empty!');
}

Upvotes: 74

user3024615
user3024615

Reputation: 111

Trim your String value by creating a trim function

var text = "  ";
if($.trim(text.length == 0){
  console.log("Text is empty");
}
else
{
  console.log("Text is not empty");
}

Upvotes: 1

Shehzad
Shehzad

Reputation: 2940

You can Trim your String value by creating a trim function for your Strings.

String.prototype.trim = function () {
    return this.replace(/^\s*/, "").replace(/\s*$/, "");
}

now it will be available for your every String and you can use it as

str.trim().length// Result will be 0

You can also use this method to remove the white spaces at the start and end of the String i.e

"  hello  ".trim(); // Result will be "hello"

Upvotes: 9

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