Examples from a blog post about closures in Javascript

example1.js

// This function accepts either an array or a single value and
// returns an array of the values that didn't match the string
// provided in argument #2
function y (myvar,str) {
    // this variable will be returned from this function
    var collection = [];

    // Check if the provided variable is an array or not
    if (myvar instanceof Array) {
        // iterate through all elements and check if they
        // match the string provided as the second argument
        for (var i = 0; i < myvar.length; i++) {
            if (myvar[i] != str) {
                collection.push(myvar[i]);
            }
        }
    } else {
        // it's not an array, just check on the one value
        if (myvar != str) {
            collection.push(s);
        }
        cl(myvar,collection);
    }
    return collection;
}

example2.js

// now the same function uses a closure to implement the
// functionality of checking and adding the variable to the
// returned array
function y (myvar,str) {
    // define the variable we'll return and a closure that will
    // determine if the string would match or not and adds it
    // to the collection array if it does not
    var collection = [],
        cl = function (s) {
            if (s != str) {
                collection.push(s);
            }
        };

    // if it's not an array, we'll just call the function on
    // the single element, but if it is, we'll call it on all
    // the elements of the array
    if (myvar instanceof Array) {
        for (var i = 0; i < myvar.length; i++) {
            cl(myvar[i]);
        }
    } else {
        cl(myvar);
    }
    return collection;
}

example3.js

function ret (a) {
    return function (somevar) {
        return somevar === a;
    }
}

b = ret("some string");

b("other string");
b("some string");

example4.js

function ret (a) {
    return function ($somevar) {
        // we're assuming it's a jQuery object
        return somevar.is(a);
    }
}

is_hidden = ret(':hidden');
is_checked = ret(':checked');

is_hidden($('.mydiv'));
is_checked($('input.myinput'));

example5.js

function all_elements_match (arr, func) {
    var ret = [];
    // Loop through all elements of the array and call the
    // callback which will tell the function if the element
    // should be added to the array or not
    for (var i = 0, l = arr.length; i < l; i++) {
        if (func(arr[i])) {
            ret.push(arr[i]);
        }
    }
    return ret;
}

var fruit = ["apple","orange","mango","grape","avacado"];

// return an array of all the fruit that start with the
// letter "a"
all_elements_match(fruit, function (element) {
    return element.match(/^a.*/) !== null;
});
// will return ["apple", "avacado"]

// return an array of all the fruit that have more than
// 5 letters in their name
all_elements_match(fruit, function (element) {
    return element.length > 5;
});
// will return ["orange","avacado"]