CODEWITHSUNDEEP
javascriptfunctionparameterscallback
Taylor's Designs
Taylor's Designs

Reputation: 57

What are the brackets after a call to a Javascript function doing?

So I found this script online, and I understand all except for 2 parts:

1) var first = getUrlVars()["id"]; var second = getUrlVars()["page"];

I've never seen a function with brackets after it, what does it mean/do?

2) function(m,key,value)

Where are these parameters coming from (m, key, value)?

window.location would be: http://papermashup.com/index.php?id=123&page=home

function getUrlVars() {
var vars = {};
var parts = window.location.href.replace(/[?&]+([^=&]+)=([^&]*)/gi, function(m,key,value) {
vars[key] = value;
});
return vars;
}

var first = getUrlVars()["id"];
var second = getUrlVars()["page"];

alert(first);
alert(second);

Upvotes: 1

Views: 281

Answers (3)

Has QUIT--Anony-Mousse
Has QUIT--Anony-Mousse

Reputation: 77454

The () are a method invocation.

The method returns a dictionary object (initialized as var vars = {}). With vars["something"] you do a dictionary lookup to retrieve data from the returned object.

You can rewrite ypur code to a faster version:

var dict = getUrlVars(); // Build dictionary (method invocation)
var first = dict["id"]; // Lookup
var second = dict["page"]; // Lookup

Shorter code is neither faster, nor more readable.

Upvotes: 0

marton
marton

Reputation: 1350

1) It's basically just chaining, you take advantage of knowing that getUrlVars will return an object, the brackets reference a property on the returned object.

2)Pretty similar logic. window.location.href returns a String, you chain the .replace() method.

function(m,key,value) is the callback you pass to replace(), it's a standard JS method, you can see the docs (with the argument descriptions) here: String.prototype.replace()

Upvotes: 0

mariocatch
mariocatch

Reputation: 8683

var first = getUrlVars()["id"];

This line is calling the getUrlVars() function, and then accessing the id property of the return object and then setting the first variable to the value of that property.

function(m,key,value) is an anonymous function passed as a parameter to the replace function on the String object. Docs here. Essentially, it's passing a function into this parameter of the replace function:

A function to be invoked to create the new substring (to put in place of the substring received from parameter #1). The arguments supplied to this function are described in the "Specifying a function as a parameter" section below.

Upvotes: 5

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