JavaScript Basics
Closure
Let's take a counter example, we are incrementing the count on the click of a button. This counter variable lives in the event listener function. The blinder variable will die once the code is run. The counter variable lives because it is used in the event listener function.
<span class=’count’>0</span>
<button class=’btn’>Click</button>let counter = 0;
let blinder = 1;
document.querySelector(‘.btn’).addEventListener(‘click’, function(){
counter++;
document.querySelector(‘.count’).innerText=counter;
});
Pass by Reference
You can pass an object as a parameter and change the values in the object.
let obj = {
a : 1,
b: 2,
c: 3
}
function parse(b){
obj.a =2;
obj.b=3;
obj.c =4;
};
console.log(‘before’, obj);
parse(obj);
console.log(‘after’, obj);
Pass by Value
For Strings, Numbers there are pass by values only. Changing the value does not affect the actual number.
let sampleValue = 9;
function changeValue(sampleValue){
sampleValue= 15;
console.log(‘In fun’,sampleValue);
}
console.log(‘Before’,sampleValue)
changeValue(sampleValue)
console.log(‘After’,sampleValue)
Changing the Reference
In the below sample we have passed the reference and added new data to it. So the actual reference data is changed
let arr =[1,3,4];
function pushToArr(arr){
arr.push(10);
}
console.log(‘Before’,arr);
pushToArr(arr);
console.log(‘After’,arr);
In the below example we have changed the reference itself so the array is not changed
let secondarr =[1,3,4];
function changeArr(secondarr){
secondarr =[1,3,4,10];
}
console.log(‘Before’,secondarr);
changeArr(secondarr);
console.log(‘After’,secondarr);
