The method given in the ECMAScript standard to find the class of Object is to use the toString method from Object.prototype.
if(Object.prototype.toString.call(someVar) === '[object Array]') {
alert('Array!');
}
Or you could use typeof to test if it is a string:
if(typeof someVar === 'string') {
someVar = [someVar];
}
Or if you're not concerned about performance, you could just do a concat to a new empty Array.
someVar = [].concat(someVar);
There's also the constructor which you can query directly:
if (somevar.constructor.name == "Array") {
// do something
}
Check out a thorough treatment from T.J. Crowder's blog, as posted in his comment below.
Check out this benchmark to get an idea which method performs better: http://jsben.ch/#/QgYAV
From @Bharath, convert a string to an array using ES6 for the question asked:
const convertStringToArray = (object) => {
return (typeof object === 'string') ? Array(object) : object
}
Suppose:
let m = 'bla'
let n = ['bla','Meow']
let y = convertStringToArray(m)
let z = convertStringToArray(n)
console.log('check y: '+JSON.stringify(y)) . // check y: ['bla']
console.log('check y: '+JSON.stringify(z)) . // check y: ['bla','Meow']
Videos
The method given in the ECMAScript standard to find the class of Object is to use the toString method from Object.prototype.
if(Object.prototype.toString.call(someVar) === '[object Array]') {
alert('Array!');
}
Or you could use typeof to test if it is a string:
if(typeof someVar === 'string') {
someVar = [someVar];
}
Or if you're not concerned about performance, you could just do a concat to a new empty Array.
someVar = [].concat(someVar);
There's also the constructor which you can query directly:
if (somevar.constructor.name == "Array") {
// do something
}
Check out a thorough treatment from T.J. Crowder's blog, as posted in his comment below.
Check out this benchmark to get an idea which method performs better: http://jsben.ch/#/QgYAV
From @Bharath, convert a string to an array using ES6 for the question asked:
const convertStringToArray = (object) => {
return (typeof object === 'string') ? Array(object) : object
}
Suppose:
let m = 'bla'
let n = ['bla','Meow']
let y = convertStringToArray(m)
let z = convertStringToArray(n)
console.log('check y: '+JSON.stringify(y)) . // check y: ['bla']
console.log('check y: '+JSON.stringify(z)) . // check y: ['bla','Meow']
In modern browsers you can do:
Array.isArray(obj)
(Supported by Chrome 5, Firefox 4.0, Internet Explorer 9, Opera 10.5 and Safari 5)
For backward compatibility you can add the following:
// Only implement if no native implementation is available
if (typeof Array.isArray === 'undefined') {
Array.isArray = function(obj) {
return Object.prototype.toString.call(obj) === '[object Array]';
}
};
If you use jQuery you can use jQuery.isArray(obj) or $.isArray(obj). If you use Underscore.js you can use _.isArray(obj).
If you don't need to detect arrays created in different frames you can also just use instanceof:
obj instanceof Array
There are several ways of checking if an variable is an array or not. The best solution is the one you have chosen.
variable.constructor === Array
This is the fastest method on Chrome, and most likely all other browsers. All arrays are objects, so checking the constructor property is a fast process for JavaScript engines.
If you are having issues with finding out if an objects property is an array, you must first check if the property is there.
variable.prop && variable.prop.constructor === Array
Some other ways are:
Array.isArray(variable)
Update May 23, 2019 using Chrome 75, shout out to @AnduAndrici for having me revisit this with his question
This last one is, in my opinion the ugliest, and it is one of the slowest fastest. Running about 1/5 the speed as the first example. This guy is about 2-5% slower, but it's pretty hard to tell. Solid to use! Quite impressed by the outcome. Array.prototype, is actually an array. you can read more about it here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray
variable instanceof Array
This method runs about 1/3 the speed as the first example. Still pretty solid, looks cleaner, if you're all about pretty code and not so much on performance. Note that checking for numbers does not work as variable instanceof Number always returns false. Update: instanceof now goes 2/3 the speed!
So yet another update
Object.prototype.toString.call(variable) === '[object Array]';
This guy is the slowest for trying to check for an Array. However, this is a one stop shop for any type you're looking for. However, since you're looking for an array, just use the fastest method above.
Also, I ran some test: http://jsperf.com/instanceof-array-vs-array-isarray/35 So have some fun and check it out.
Note: @EscapeNetscape has created another test as jsperf.com is down. http://jsben.ch/#/QgYAV I wanted to make sure the original link stay for whenever jsperf comes back online.
You could also use:
if (value instanceof Array) {
alert('value is Array!');
} else {
alert('Not an array');
}
This seems to me a pretty elegant solution, but to each his own.
Edit:
As of ES5 there is now also:
Array.isArray(value);
But this will break on older browsers, unless you are using polyfills (basically... IE8 or similar).
I am logging type of a variable which is an array, if it is empty or has one element console shows Array(), however if variable length is greater than 1 it shows object. And when it is object proto is still Array of length zero.