flattenArray.js

/* 
In ruby I could just do:

    our_arr = in_arr.flatten

But that says more about ruby than it does about me.
*/


/* flatten returns a new array that is a flattened 
 * version of the array passed in, runs recursively.
 * 
 * inArr - The array to be flattened
 */
function flatten(inArr) {
    var outArr = [];
    inArr.forEach(function(el) {
        /* Array.isArray is an ES5 feature */
        if (Array.isArray(el)) {
            outArr = outArr.concat(flatten(el));
        } else {
            outArr.push(el);
        }
    });
    return outArr;
}

/* I'm provding a function here that tests/demonstrates the flatten function above.
 * Returns a boolean indicating the test pass status. */
function testFlatten() {
    //tests is an array of objects, each with an input and an expected output
    var tests = [{ 
        input : [[1,2,[3]],4],
        expected : [1,2,3,4]
    }, {
        input : [[]],
        expected : []
    }, {
        input : [1,2,3,[3],1,[1,[2,[3,3,[[3]]]]]],
        expected : [1,2,3,3,1,1,2,3,3,3]
    }];

    var passed = true;
    tests.forEach(function(test, i) {
        //This comparison technique works for comparing 1-d arrays of integers.
        if (JSON.stringify(flatten(test.input)) === JSON.stringify(test.expected)) {
            console.log("Test Passed:", i+1);
        } else {
            console.log("Test Failed:", i+1);
            passed = false;
        }
    });
    return passed;
}