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02-for-loops-and-arrays.js
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02-for-loops-and-arrays.js
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var assert = require('assert');
var ___ = undefined;
/*
* To complete the exercise, replace underscores in the
* code below with appropriate values to make the tests
* pass.
*
* See README.md for installing the test library and
* running the tests.
*/
describe("Arrays", function(){
it("can be defined", function(){
assert( ___ instanceof Array);
});
it("have a length", function(){
var arr = [];
assert.strictEqual(arr.length, ___);
});
it("can be accessed using the index notation", function(){
var arr = ["hello", 42, "Blueberry pie", [6, 7]];
assert.strictEqual(arr[0], ___);
assert.strictEqual(arr[1], ___);
assert.strictEqual(arr[2], ___);
assert.strictEqual(arr[3], ___);
});
it("can be nested inside each other", function(){
var arr2D = [
['a1', 'b1', 'c1'],
['a2', 'b2', 'c2'],
['a3', 'b3', 'c3']
];
assert.strictEqual(arr2D[0][0], ___);
assert.strictEqual(arr2D[2][2], ___);
assert.strictEqual(arr2D[0][2], ___);
assert.strictEqual(arr2D[2][0], ___);
});
it("can have an element added using 'push()'", function(){
var arr = [1,2,3];
arr.push("Gooseberry");
assert.deepStrictEqual(arr, ___);
});
it("can have an element removed using 'pop()'", function(){
var arr = [1,2,3];
arr.pop();
assert.deepStrictEqual(arr, ___);
});
});
describe("The for loop", function(){
it("will do something a number of times", function(){
var xs = [];
for ( var x = 0; x < 10; x++){
xs.push(x);
}
assert.deepStrictEqual(xs, ___);
});
it("has an initialiser expression", function(){
var xs = [];
for ( var x = 5; x < 10; x++){
xs.push(x);
}
assert.deepStrictEqual(xs, ___);
});
it("has a loop condition", function(){
var xs = [];
for ( var x = 5; x < 12; x++){
xs.push(x);
}
assert.deepStrictEqual(xs, ___);
});
it("has an update expression", function(){
var xs = [];
for ( var x = 5; x < 12; x=x+2){
xs.push(x);
}
assert.deepStrictEqual(xs, ___);
});
it("can get quite complex", function(){
// This is horrible :-)
//
// However, once you can complete this test,
// for loops will no longer hold any mysteries for you.
//
// Try to go through it on paper with a column for each
// variable and the loop condition.
//
// If you can't do it, don't worry we'll go through it
// together on the whiteboard
var xs = [];
for(var i=3, j=5; i<20 && j>0; i=j+i, j=(j+i)/2 ){
xs.push([i,j]);
}
assert.deepStrictEqual(xs, ___);
});
});
describe("Array iteration", function(){
// Note that in most of these examples, using map
// would have been clearer. That's okay though, we
// are doing this to learn about arrays and looping.
// I'd expect to see arr.map(function(e){...}) in
// production code to solve the same problems though.
//
// TL;DR – Don't worry about this comment.
it("can be done with a for loop", function(){
var arr = [1,2,3,4,5];
var xs = [];
for (var i = 0; i < arr.length; i++){
xs.push(arr[i]*arr[i]);
}
assert.deepStrictEqual(xs, ___);
});
it("can be done backwards", function(){
var arr = [1,2,3,4,5];
var xs = [];
for (var i = ___; i >= 0; i--){
xs.push(arr[i]);
}
assert.deepStrictEqual(xs, [5,4,3,2,1]);
});
it("can be done only for every other number", function(){
var arr = [1,2,3,4,5];
var xs = [];
for (var i = 0; i < arr.length; i=___){
xs.push(arr[i]);
}
assert.deepStrictEqual(xs, [1,3,5]);
});
it("can be done using the Array's forEach method", function(){
var arr = [1,2,3,4,5];
var xs = [];
arr.forEach(function(element){
___;
});
assert.deepStrictEqual(xs, [3,5,6,7,8]);
});
});