built-in-functions.js

/* 
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 Tutorial: JavaScript's common built-in functions 
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*/

/* 
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 BUILT-IN FUNCTIONS: global, built-in JavaScript functions that can be called on objects 
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 COMMON FUNCTIONS: 
 - parseInt() & parseFloat()
 - map()
 - Math.round()
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 SYNTAX:
 func() - can be called anywhere, as an input, as a variable, acts like a normal function
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*/



/*
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 parseInt(): accepts a parameter of a string (of a number) and returns the integer
 parseFloat(): accepts a parameter of a string (of a decimal number) and returns the decimal number
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*/

// EXAMPLES

/* here you can see that we can add because integerString is 
converted into a number */
const integerString = "100";
console.log(parseInt(integerString) + 50);

/* the same applies to parseFloat() */
const floatString = "100.5";
console.log(parseFloat(floatString) + 50.5);



/*
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 map(): creates a new array from an old array with changes of a function
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*/

// EXAMPLE

/* here we iterate through an array of numbers, creating a new array with the original
numbers multiplied by 10 with an arrow function (could also be an arrow function) */
const numbersArray = [4, 500, 3.5];
console.log(numbersArray.map(function(input) {return input * 10;}));

/* you can also call a function (reference it without parentheses so that it can be used
as a callback) in map() */
function multiply(input) {
    return input * 10;
}
console.log(numbersArray.map(multiply));



/*
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 Math.round(): rounds normamlly a decimal number to the nearest integer (.5 & up goes to next number)
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*/
// EXAMPLE

/* notice here how we have to reference the Math object in order to access the round function */
const num = 45.3;
console.log(Math.round(num));



/*
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 Challenge: create an array "output" which holds the output of mapping through an array 
 of floating numbers (as strings) and rounds them to the nearest integer

 -> use console.log() on the variable "output" to show the array with rounded numbers
 -> the array of floating numbers as string should be named "input"
 -> the input array can be of any size
 -> use an anonymous function (function() {}) inside of map()
 -> the parameter inside this anonymous function should be "num"
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*/