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How to create different array's value while looping?

when i load this function the value of the array's all the same .. How can i make different array's value everytime i load this function ? btw the num1, num2, opt1, opt2 .. is a random number from
random = () => {
return Math.floor(Math.random() * 15)
}
please help me guys :)this is my code ..
makeQuestion = () => {
questions = [];
for(var i = 0; i < 4; i++){
var obj = {
'question': `Berapakah ${num1} ${operator} ${num2} ?`,
'choice1' : `${opt1}`,
'choice2': `${opt2}`,
'choice3': `${opt3}`,
'choice4': `${final}`,
'answerIndex' : `${2}`,
}
questions.push(obj)
}
}

JavaScript how to transform String into a function

I am doing a calculator for definite integrals, where I can add the function to integrate by using this interface.Calculator interface
The point is that once I call the function to integrate it recognizes it as a String and i cannot calculate over it. But if I add the function hardcoding it, it works perfectly fine.
prueba() {
//**** this.cadena is the function I add by using the interface
var sal = this.cadena;
console.log(sal);
var f = function (x) {
//**** The comented return works perfecly fine
//return 1/x;
return parseFloat(sal);
};
var integrada = this.integ(sal, 1, 2);
this.cadena = integrada;
this.imprime();
}
integ(f, a, b) {
var area = 0;
var dx = 0.001;
for (let x = a; x < b; x += dx) {
area += dx * f(x);
}
return area;
}

Can you try below line
var integrada = this.integ(parseFloat(sal), 1, 2);

variable copies wrong content js

This is all the js code, when i console log the raw variable it returns the shuffled deck, I do not understand that, i am new to js and i've tried this. but i don't really know how it works, also, what's the difference between var and let if you guys dont mind me asking? thank you.
function drawDeck(){
var deck = []
var value = [2,3,4,5,6,7,8,9,10,10,10,10,11]
for(var i=0;i<4;i++){
for (var j=0;j<13;j++){
deck.push(value[j])
}
}
return deck
}
function shuffleDeck(deck){
var currentPos = deck.length, tempPos , randPos
while (currentPos != 0){
randPos = Math.floor(Math.random() * currentPos)
currentPos -= 1
tempPos = deck[currentPos]
deck[currentPos] = deck[randPos]
deck[randPos] = tempPos
}
return deck
}
function drawCard(deck){
var card = deck.shift()
return card
}
var raw = drawDeck()
var deck = shuffleDeck(raw)
var card = drawCard(deck)
console.log(raw)

The shuffle function operates on the input element itself. Since you input raw to the shuffle function it self will be modified and thus you get the shuffled deck when logging it. It doesn't matter if it gets returned or not.
If you wanna preserve the original array, clone the array to a new variable inside the shuffle function and do the shuffling on the clone and return that.
var raw = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16];
var shuffled;
function shuffleDeck(deck) {
var currentPos = deck.length,
tempPos, randPos
var tempDeck = Array.from(deck);
while (currentPos != 0) {
randPos = Math.floor(Math.random() * currentPos)
currentPos -= 1
tempPos = tempDeck[currentPos]
tempDeck[currentPos] = tempDeck[randPos]
tempDeck[randPos] = tempPos
}
return tempDeck
}
shuffled = shuffleDeck(raw);
alert('original: ' + raw);
alert('shuffled: ' + shuffled);

How can javascript like varName.myFunction()

function CircleArea(Value) {
var Results = 3.14 * Value^2;
return Results;
}
So I want:
var Diameter = 30;
Diameter.CircleArea(); // Results 2826
Like:
var n = 30; n.toString() // Results 30
Syntax:
varName.myFunction();

You can but rarely should extend prototypes:
Number.prototype.circleArea = function() {
var value = this;
return Math.pow(value, 2) * Math.PI;
};
var num = 30;
console.log(num.circleArea()); // 2827.4333882308138

Your function accepts an argument .
So you will need to pass in Diameter like so :
CirclArea(Diameter)
Returns 2826

How to give a variable a random value in javascript

How would I give a variable a random value in javascript?
I can do this:
var myMake = ["Chevy","Subaru","Kia","Honda","Toyota"];
var x = Math.floor(Math.random() * 4 + 1);
var rand = myMake[x];
alert(rand);
which gets the desired effect, giving the variable rand a random value of one of these:
Chevy, Subaru, Kia, Honda, Toyota
but would there be a way to make a function/method that does something like this?:
var rand = randVal("Chevy", "Subaru", "Kia", "Honda", "Toyota");
Thanks!!

function randVal(){
var x = Math.floor(Math.random() * arguments.length);
return arguments[x];
}
the arguments is an array like object that refers gives a list of all supplied arguments to a function.

Just to be different!
var x = ["Chevy","Subaru","Kia","Honda","Toyota"].sort(function() {
return 0.5 - Math.random();
})[0];
alert(x);
jsfiddle
And as a function, but accepting an Array
var randMe = function ( me ) {
if ( me ) {
return me.sort(function() {
return 0.5 - Math.random();
})[0];
}
}
alert(randMe(['a','b','c']));
jsfiddle
And some prototyping as well
Array.prototype.rand = function() {
return this.sort(function() {
return 0.5 - Math.random();
})[0];
}
alert(['a','b','c'].rand());
jsfiddle
Also the actual shuffle function from here.

You can do that very easy with jQuery:
(function($) {
$.rand = function(arg) {
if ($.isArray(arg)) {
return arg[$.rand(arg.length)];
} else if (typeof arg === "number") {
return Math.floor(Math.random() * arg);
} else {
return 4; // chosen by fair dice roll
}
};
})(jQuery);
var items = ["Chevy","Subaru","Kia","Honda","Toyota"];
var item = $.rand(items);