Check if a variable is a string in JavaScript
我怎样才能确定一个变量是一个字符串或JavaScript中的其他东西？
You can use typeof operator:
var booleanValue = true;
var numericalValue = 354;
var stringValue = "This is a String";
alert(typeof booleanValue) // displays "boolean"
alert(typeof numericalValue) // displays "number"
alert(typeof stringValue) // displays "string"
Example from this webpage. (Example was slightly modified though).
Here's reference for typeof operator.
这对我很有用：
if (typeof myVar === 'string' || myVar instanceof String)
// it's a string
else
// it's something else
Since 580+ people have voted for an incorrect answer, and 800+ have voted for a working but shotgun-style answer, I thought it might be worth redoing my answer in a simpler form that everybody can understand.
function isString(x) {
return Object.prototype.toString.call(x) === "[object String]"
}
Or, inline (I have an UltiSnip setup for this):
Object.prototype.toString.call(myVar) === "[object String]"
FYI, Pablo Santa Cruz's answer is wrong, because typeof new String("string") is object
DRAX's answer is accurate and functional, and should be the correct answer (since Pablo Santa Cruz is most definitely incorrect, and I won't argue against the popular vote.)
However, this answer is also definitely correct, and actually the best answer (except, perhaps, for the suggestion of using lodash/underscore). disclaimer: I contributed to the lodash 4 codebase.
My original answer (which obviously flew right over a lot of heads) follows:
I transcoded this from underscore.js:
['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp'].forEach(
function(name) {
window['is' + name] = function(obj) {
return toString.call(obj) == '[object ' + name + ']';
};
});
That will define isString, isNumber, etc.
In Node.js, this can be implemented as a module:
module.exports = [
'Arguments',
'Function',
'String',
'Number',
'Date',
'RegExp'
].reduce( (obj, name) => {
obj[ 'is' + name ] = x => toString.call(x) == '[object ' + name + ']';
return obj;
}, {});