javascript“或”-它们可以组合成一个数组吗？

Question

wondering if I can make my javascript more efficient. I have a var JSP = "the jsp's name"

And I have statements in a javascript validation file:

if(( JSP == "test.html" ) || ( JSP == "test1.html") || ( JSP == "test2.html" )) then blah blah blah.

Is there a more efficient way to do this?

Answer 1

If you know that JSP contains a string, it's slightly more efficient to use === rather than == . Also note that you don't need all those parens:

if (JSP === "test.html" || JSP === "test1.html" || JSP === "test2.html") {
    // do something
}

You could also use a regular expression:

if (/^test[12]?\.html$/.test(JSP)) {
    // do something
}

...but it depends what you mean by "efficient." The series of === will be very efficient at runtime.

Separately, you could use a switch :

switch (JSP) {
    case "test.html":
    case "test1.html":
    case "test2.html":
        // Do it
        break;
}

...but I wouldn't call it more efficient.

I definitely would not put the options in an array, because searching through the array will not be efficient. But you can use a map:

var pages = {
    "test.html":  true,
    "test1.html": true,
    "test2.html": true
};

...and then this test:

if (pages[JSP] === true) {
    // do something
}

...which results in a fairly efficient property lookup. That's only reasonable if you create the object once and reuse it.

(You might have people say "Or just use if (pages[JSP]) { ... } . But that fails if JSP happens to contain "toString" or "valueOf" or any of several other inherited properties blank objects get from Object.prototype . It's fine if you're certain it won't have any of those values, though.)

Answer 2

You could create an object with those keys:

var theThings = { "test.html": true, "test1.html": true, "test2.html": true };

if (theThings[JSP]) { /* whatever */ }

If there are only three or four, it might not be worth it, but if there are dozens it'd definitely be faster, especially if the test gets made several times.

edit — wow I'm crying a little inside here, guys. Property name lookups are going to be way faster than linear searches through an array.

Answer 3

var arr = ['test.html', 'test1.html', 'test2.html'];
if (arr.indexOf(JSP)) != -1) {
   alert("found it!");
}

relevant docs here .

Answer 4

if( JSP in {"test.html":0, "test2.html":0, "test3.html":0} ) {
...
}

It doesn't get any closer to SQL's IN( 1, 2, 3) than this in javascript :-)

Answer 5

if (["test.html", "test1.html", "test2.html"].indexOf(JSP) > -1)

对于不支持数组上的indexOf浏览器， MDC建议使用短代码来添加缺少的功能。

Answer 6

Probably not more efficient, but you got cleaner ways to do it. You could for instance use a switch-case like this:

switch(JSP) {
    case 'test.html':
    case 'test1.html':
    case 'test2.html':
    blablabla; break;
}

Or you could create an array out of the urls and see if your string is in the array like this

var arr = [
    'test.html', 'test1.html',
    'test2.html'
];
if(arr.indexOf(JSP) != -1) { blablabla; }

The last one will not work in all browsers.

Answer 7

A way of doing it in jQuery is to use the inArray method, eg:

if ($.inArray(JSP, ["test.html", "test1.html", "test2.html"]) > -1) {
    // your code
}

The inArray method works in a similar manner to String.indexOf so -1 is returned if no match.

Answer 8

Use a regular expression?

if (/^test\d?\.html$/.test(JSP)) { ... }

I can't promise that will be more efficient though, just tidier code-wise.

Or if you're already using jQuery, you could use jQuery.inArray():

var names = ['test.html', 'test2.html', 'test3.html'];
if ($.inArray(JSP, names)) { ... }

Or with underscore.js

var names = ['test.html', 'test2.html', 'test3.html'];
if (_.indexOf(names, JSP) !== -1) { ... }