Functions

Coding Challenge Console Quiz

function generator(input){
 var number= input;
 return function(){
 return number * 2;
};
}

Call function

var calc = generator(900);
console.log(calc());

Passing Functions as Arguments

var years = [1950, 1950, 1958, 1967];

function arrayCalc(arr, fn) {
    //empty function to hold return
    var arrRes = [];
    for (var i = 0; i < arr.length; i++) {
        // this takes the calculateAge2 function(i) and for each i 
        // it calculates the age and push it to the array which is returned.
        arrRes.push(fn(arr[i]));
    }
    return arrRes;
}

function calculateAge2(el) {
    return 2016 - el;
}
// the calculateAge2 does not have the () because we don't want to call it there
// its called a callback function because it is called when it's passed to the other function

var ages = arrayCalc(years, calculateAge2);
function isFullAge(el) {
    return el >= 18;
}
console.log(ages);

Another Call Back function using the function above, this calculates the optimal heart rate based on a persons age

function maxHeartRate(el) {
    if (el >= 18 && el <= 81) {
        return Math.round(206.9 - (0.67 * el));

    } else {
        return -1;
    }

} // maxHeartRate
var rates = arrayCalc(ages, maxHeartRate);
console.log(rates);

Functions Returning Functions

function interviewQuestion(job) {
    if (job === 'designer') {
        return function(name) {
            console.log(name + " Explain UX");
        }
    } else if (job === 'teacher') {
        return function(name) {
            console.log(name + ', What subject do you teach');
        }

    } else {
        return function(name) {
            console.log(name + ' what do you do');
        }
    }
} // interviewQuestion

var teacherQuestion = interviewQuestion('teacher');
teacherQuestion('john');

var designerQuestion = interviewQuestion('designer');
designerQuestion('john');

Another way to call the function without a variable

interviewQuestion('teacher')('mark');

line is evaluated from left to right, teacher is called first returning a function then mark is passed into that function.

Closures

Same Program as above but written using closures.
Closures is basically making variables private.

function interQ(job) {

    return function(name) {
        if (job === 'designer') {
            console.log(name + " Explain UX");

        } else if (job === 'teacher') {
            console.log(name + ', What subject do you teach');
        } else {

            console.log(name + ' what do you do');
        }
    }
}

interQ('teacher')('Robert');

Bind Call and Apply Methods

Call Function Also know as Method Borrowing

Allow you to call a function and set the this variable manually
A John object is created with a presentation function, along with other attributes.
We are now going to create another object Emily with a few attributes, but without the presentation function, However we would like to use that function with the Emily Object.

var john = {
        name: 'John',
        age: '26',
        job: 'teacher',
        presentation: function(style, timeOfDay) {
                if (style === 'formal') {
                    console.log(
                        'Good ' + timeOfDay + ', Ladies and Gents I\'m ' + this.name + ' Job is ' +
                        this.job + ' and years old ' + this.age
                    );
                } else if (style == 'friendly') {
                    console.log(
                        'Whats Up ' + timeOfDay + ', Dudes I\'m ' + this.name + ' Job is ' +
                        this.job + ' and years old ' + this.age
                    );
                } // end else if
            } // presentation
    } // end john

Call the John Object

john.presentation('formal', 'morning');
john.presentation('friendly', 'evening');

Create a new Emily object

var emily = {
        name: 'emily',
        age: '29',
        job: 'designer',

    } // end emily

Call the Emily object Utilizing the presentation function form john. This call() function allows the 'this' keyword to be applicable to Emily and not the john object
The First argument of the call() function is the 'this' which in this case is emily.

john.presentation.call(emily, 'friendly', 'afternoon');

Bind Method

Same as the call() but it doesn't call the function right away but creates a copy of it. It allows you to preset some parameters passed to the internal function

var johnFriendly = john.presentation.bind(john, 'friendly');
johnFriendly('morning');
johnFriendly('night');

The Presentation function was preset with 'friendly' argument An example using emily. The emily is the "this"

var emilyFormal = john.presentation.bind(emily, 'formal');
emilyFormal('formal');

Another Example of the bind method Applied to the Earlier Example

var years = [2001, 1950, 1958, 1967];

function arrayCalc(arr, fn) {
    //empty function to hold return
    var arrRes = [];
    for (var i = 0; i < arr.length; i++) {
   
        arrRes.push(fn(arr[i]));
    }
    return arrRes;
}

function calculateAge2(el) {
    return 2016 - el;
}

function isFullAge(limit, el) {
    return el >= limit;
}


var ages = arrayCalc(years, calculateAge);
var fullJapan = arrayCalc(ages, isFullAge.bind(this, 20));

By binding the isFullAge, we are able to pass the preset of 20 into the arrayCal function.

Apply Method

Same as the bind Method but the arguments are passed as an array.
john.presentation.apply(emily, ['friendly', 'afternoon'])'

Timers and Intervals

setTimeout(function(){
console.log('finished');
},2000);

Intervals - will run ever 5 seconds

setInterval(function(){
console.log('ping');
},500);

Interval will stop

var interval = setInterval(function(){
console.log('ping');
});

setTimeout(function(){
clearInterval(interval);
},2500);

Immediately Invoked Functions

(function() {
var score = Math.random() * 10;
console.log(score >=5);
})();

Passing an argument into the function

(function(goodluck) {
var score = Math.random() * 10;
console.log(score >=5 - goodluck);
})(5);

Adding the 5 in the closing parenthesis will pass it as an argument

Transforming Format and Values

parseInt();
toFixed(3) rounds to 3 decimal places

String Functions

a = "abc";
a.length;
a[2]; = c
a.charAt(2); = c
a.concat('add to string');
a.toUpperCase();
a.split(' '); will split string using supplied delimiter into a array;
a.trim() // trim white space before and after a string.

Sorting Numbers

Will work on numbers only

var numbers=[11,2,3,33];

var sortAscending = function(x,y){
  return x -y;
}
console.log(numbers.sort(sortAscending));

Will work on numbers and text

var numbers=[11,2,3,33];

var sortAscending = function(x,y){
  if(x > y) return 1;
  if(y>x) return -1;
 return 0;
}
console.log(numbers.sort(sortAscending));

Sort Descending

Will work on numbers and text

var numbers=[11,2,3,33];

var sortAscending = function(x,y){
  if(x > y) return -1;
  if(y>x) return 1;
  return 0;
}
console.log(numbers.sort(sortAscending));