如何使用underscore.js查找String是否为空？

Question

我看起来相当于http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html#isBlank(java.lang.CharSequence）我发现了几个第三方扩展，但是有一个开箱即用的下划线.js： http ： //underscorejs.org

Answer 1

Following @muistooshort's advice I created my mixin and wanted to share it:

  _.mixin({
    isBlank: function(string) {
      return (_.isUndefined(string) || _.isNull(string) || string.trim().length === 0)
    }
  });

> _("\t").isBlank()
< true

> _("qwerty").isBlank()
< false

Answer 2

_.isEmpty(_.trim(string));

This runs a null or empty string check.

Edited with update from ehftwelve

Answer 3

function isBlank(str) {
  return !!(str||'').match(/^\s*$/);
}

isBlank(null);    // => true
isBlank('');      // => true
isBlank(' \t ');  // => true
isBlank(' foo '); // => false

Answer 4

In Underscore.js you have _.isEmpty ( http://underscorejs.org/#isEmpty ) but it only checks if the array-like object or string has a length of 0.

If you want to check if a variable is a whitespace string, empty string or null (equivalent of java's isBlank) you should make your own function.

function isBlank(str) {

  if (str === null || str.length === 0 || str === " ") return true;
  return false;

}

Answer 5

using bind to create a native method:

var isBlank=/./.test.bind(/(^$)|(^null$)|(^\s+$)/); // bind a regexp to test()

_.map(["", " ", " x ", 0, null], isBlank ); // test it against various data
// == [true, true, false, false, true] // reflects java version output

Answer 6

You could extend underscore.

  _.isBlank = function (str) {
        return !!(str||'').match(/^\s*$/);
    }

If you really don't want to create a function as taseenb mentioned use isEmpty with trim. Although this is ugly!

_.isEmpty('    '.trim());

Although both these don't work with tabbed spaces

Answer 7

Here's my snippet that I used when checking empty strings.

    _.isBlank = function (str) {
       return (!str || /^\s*$/.test(str));
    }

    var strs = ['a', 1, -1, 0, NaN, '', ' ', '\t', '\n', null, undefined];
    strs.forEach(function(s){
     console.log('is blank? ', s, _.isBlank(s));
    });

Note: The zero(0) will be considered as empty.