string.match（）返回String而不是Array

Question

I've been using Javascript string.match(*regex*) function to parse the navigator.userAgent string.

FYI, According to MDN & W3schools:

"The match() method searches a string for a match against a regular expression, and returns the matches, as an Array object ."

I first parse once to get the wanted strings for the base string:

var userAgent = navigator.userAgent;
var splitted = userAgent.match(/[(][^)]+[)]|\w+\/\S+/ig);

Which gives me the following Output (Which is an Array)

Mozilla/5.0
(Macintosh; Intel Mac OS X 10_10_3)
AppleWebKit/537.36
(KHTML, like Gecko)
Chrome/41.0.2272.76
Safari/537.36

Then i parse the Navigator/Version type strings in a for loop

for (var i = 0; i < splitted.length; i++ ) {
    var str = splitted[i];
    if (str[0] == '(') {
    } else {
        var name = str.match(/[^\/]+/i);
        var version = str.match(/[0-9|\.]+/i);
}

But, very surprisingly and even though I get the desired result, I get a String Object for the name and an Array Object for the version

How is it even possible ?

Here's the snippet of the code ( fiddle ):

 var userAgent = navigator.userAgent; var splitted = userAgent.match(/[(][^)]+[)]|\\w+\\/\\S+/ig); var outputDiv = document.getElementById("log"); for (var i = 0; i < splitted.length; i++ ) { var str = splitted[i]; if (str[0] == '(') { } else { var name = str.match(/[^\\/]+/i); var version = str.match(/[0-9|\\.]+/i); outputDiv.innerHTML += name.toString() + " is a " + typeof(name) + "<br>"; outputDiv.innerHTML += version.toString() + " is a " + typeof(version) + "<br>"; } }; 

 <div id="log"></div> 

--- UPDATE ---

Thanks FactoryAidan for the answer, it was a scope problem.

Conclusion: be careful when naming global variables :)

Answer 1

Global Variable Scope

It is because you are using name as your variable. This is a global browser window variable that is inherently a string and cannot be stored as an Array

Even if you redeclare it with var name = , you are still in the global scope. And thus name (aka window.name ) simply retains the last value you assign to it.

You can test this with the following on an empty page without defining any variables at all:

console.log(name===window.name) // Returns true
console.log(name,window.name)   // Returns 'Safari Safari' for my browser

---

Change name to something else

If you change your name variable to simply have a different name, like my_name , it stores the result of .match() as an Array.

var my_name = str.match(/[^\/]+/i);
var version = str.match(/[0-9|\.]+/i);

console.log(typeof my_name, my_name instanceof Array) // Returns object, true

---

Change Scope by wrapping in a function

This is your exact code wrapped inside a function and returns the correct variable types:

function getBrowserStuff(){

    var userAgent = navigator.userAgent;
    var splitted = userAgent.match(/[(][^)]+[)]|\w+\/\S+/ig);

    for (var i = 0; i < splitted.length; i++ ) {
        var str = splitted[i];
        if (str[0] == '(') {
        } else {
            var name = str.match(/[^\/]+/i);
            var version = str.match(/[0-9|\.]+/i);
            console.log('Name','Typeof '+(typeof name), 'IsArray '+(name instanceof Array),name)
            console.log('Version','Typeof '+(typeof version),'IsArray '+(version instanceof Array),version)
        }
    }

    return 'whatever'
}

getBrowserStuff()

---

Changing the variable name to my_name OR wrapping code like the above function returns this:

Name    Typeof object IsArray true ["Mozilla"]
Version Typeof object IsArray true ["5.0"]
Name    Typeof object IsArray true ["AppleWebKit"]
Version Typeof object IsArray true ["600.3.18"]
Name    Typeof object IsArray true ["Version"]
Version Typeof object IsArray true ["8.0.3"]
Name    Typeof object IsArray true ["Safari"]
Version Typeof object IsArray true ["600.3.18"]

Where before it returned this:

Name    Typeof string IsArray false Mozilla
Version Typeof object IsArray true  ["5.0"]
Name    Typeof string IsArray false AppleWebKit
Version Typeof object IsArray true  ["600.3.18"]
Name    Typeof string IsArray false Version
Version Typeof object IsArray true  ["8.0.3"]
Name    Typeof string IsArray false Safari
Version Typeof object IsArray true  ["600.3.18"]

Answer 2

This is not possible, or is a bug of your implementation.

According to the ECMAScript 5.1 specification, match behaves like this:

15.5.4.10 String.prototype.match (regexp)

When the match method is called with argument regexp , the following steps are taken:

1. Call CheckObjectCoercible passing the this value as its argument.
2. Let S be the result of calling ToString , giving it the this value as its argument.
3. If Type ( regexp ) is Object and the value of the [[Class]] internal property of regexp is " RegExp ", then let rx be regexp ;
4. Else, let rx be a new RegExp object created as if by the expression new RegExp( regexp ) where RegExp is the standard built-in constructor with that name.
5. Let global be the result of calling the [[Get]] internal method of rx with argument " global ".
6. Let exec be the standard built-in function RegExp.prototype.exec ( see 15.10.6.2 )
7. If global is not true , then
   1. Return the result of calling the [[Call]] internal method of exec with rx as the this value and argument list containing S .
8. Else, global is true
   1. Call the [[Put]] internal method of rx with arguments " lastIndex " and 0.
   2. Let A be a new array created as if by the expression new Array() where Array is the standard built-in constructor with that name.
   3. Let previousLastIndex be 0.
   4. Let n be 0.
   5. Let lastMatch be true .
   6. Repeat, while lastMatch is true
      1. Let resul t be the result of calling the [[Call]] internal method of exec with rx as the this value and argument list containing S .
      2. If result is null , then set lastMatch to false .
      3. Else, result is not null
         1. Let thisIndex be the result of calling the [[Get]] internal method of rx with argument " lastIndex ".
         2. If thisIndex = previousLastIndex then
            1. Call the [[Put]] internal method of rx with arguments " lastIndex " and thisIndex +1.
            2. Set previousLastIndex to thisIndex +1.
         3. Else, set previousLastIndex to thisIndex .
         4. Let matchStr be the result of calling the [[Get]] internal method of result with argument " 0 ".
         5. Call the [[DefineOwnProperty]] internal method of A with arguments ToString ( n ), the Property Descriptor {[[Value]]: matchStr , [[Writable]]: true , [[Enumerable]]: true , [[configurable]]: true }, and false .
         6. Increment n .
   7. If n = 0, then return null .
   8. Return A .

Therefore, for your global regex, the only possible returned values are null or A , which is an array.

For the non global ones, the result of calling RegExp.prototype.exec is returned. But it also returns an array or null :

Performs a regular expression match of string against the regular expression and returns an Array object containing the results of the match, or null if string did not match.