ForEach, Map, Filter, Reduce

const lol =["yo","yoo","yooo","yoooo"];
// lol.forEach((val,index,arr)=>{console.log(val,index,arr)})
// forEach returns nothing
const forEachnums =[]
const myNums =[1,2,3,4,5,6,7,8,9,10];
myNums.forEach((num)=>{
    if(num>4){
        forEachnums.push(num)
    }
})
const newNums=myNums.filter((nums)=> nums>4)

console.log(newNums)
console.log(forEachnums)
// ---------------------------------------------------------------------
const lessgo =myNums.map((num)=>num+1)
console.log(lessgo)
//----------------------------------------------------------------------
//reduce
const myTotal =myNums.reduce((acc,curr)=>acc+curr,0)
console.log(myTotal)

For In Loop

const myObjyo={
    hello:"yoyo",
    skibidi:"toilet",
    lessgo:"yy"
}
//for in loop.
// for (const key in myObjyo) {
//    console.log(`key is ${key} value is ${myObjyo[key]}`)
// }

// arr =["array","key","start","from",0]
// for (const key in arr) {
//     console.log(key)
// }

// for of -->map it also gives key and value
// for in -->object it only gives key 
// map is not iterable

For Of Loop

// for of
// const arr = [1, 2, 3, 4, 5];
// for(const i of arr){
//     console.log(i);
// }

// const greetings="hello world!";
// for(const greet of greetings){
//     if(greet!=" "){
//     console.log(`each letter is ${greet}`);}
// }

const map =new Map();
map.set("IN","INDIA")
map.set("IN","INDIA")
// console.log(map);

// for(const [key,value]of map){
//     console.log(`${key}==>${value}`)
// }

// object can’t be iterated in for of loop The for…of loop specifically looks for a special method called [Symbol.iterator] on the item you give it. Arrays have it. Strings have it. Plain objects do not have it.

1. The Error If you try for (let x of obj), JS basically checks: “Does obj have a Symbol.iterator function?” -> No. -> Throw TypeError: obj is not iterable.​
2. Why don’t they have it? (The “Why”) It’s by design. Objects are unordered collections of keys. “Iterating” implies a specific sequence (first, second, third). Since objects traditionally didn’t guarantee order (until recently with ES6 keys), there is no single “correct” way to iterate them: Should it iterate keys? Should it iterate values? Should it include hidden prototype properties? Because there’s no single right answer, JS leaves it undefined rather than guessing wrong.​

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| Method | Mutates? | Return type | Typical use | Needs callback? | | ——— | ——– | ————– | —————————- | ———————- | | forEach | No | undefined | Side effects / logging | Yes mdn2.netlify​ | | map | No | New array | Transform elements | Yes developer.mozilla​ | | filter | No | New array | Keep some elements | Yes openjavascript​ | | reduce | No | Single value | Sum, aggregate, build object | Yes geeksforgeeks​ | | find | No | Single element | First match | Yes w3schools​ | | findIndex | No | Number (index) | Index of first match | Yes w3schools​ | | some | No | Boolean | “Any element matches?” | Yes w3schools​ | | every | No | Boolean | “All elements match?” | Yes w3schools​ | | sort | Yes | Same array | Reorder elements | Yes/No openjavascript​ | | flat | No | New array | Flatten nesting | No w3schools​ | | flatMap | No | New array | Map then flatten | Yes w3schools​ |

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Object Static Methods

const myObj={
    name:"adarsh",
    age:22,
    city:"delhi"
}   
// const keys =Object.keys(myObj);
// const values =Object.values(myObj);
const entries =Object.entries(myObj);
// console.log(keys);
// console.log(values);
console.log(entries);