var pushElement=(arr,el1,el2)=>{
  arr.push(el1);
  arr.push(el2);
  return arr;
}
console.log( pushElement([1],2,3) );

var arr1=["1","2","3","4","5"];
console.log(arr1.toString());       
console.log(JSON.stringify(arr1));  

function sum1_100(){
  var sum=0,num=1;
  do{
    sum+=num;
    num++;
  }while (num<=100)
  return sum;
}
console.log(sum1_100()) 

var arr1=[1,2,3],arr2=[4,5,6];
console.log(arr1.concat(arr2));
console.log(arr1.concat(4,5,6));
console.log(arr1.concat([4],[5],[6]));
console.log(arr1.concat(...arr2));
console.log(arr1.concat(4).concat(5).concat(6)); 

var str="My name is John";
var words1=str.split(" ",3);
console.log("words1:",words1);
var words2=str.split(" ",5);
console.log("words2:",words2);

var arr=[1,2,3,11,21,31];
arr.sort((a,b)=>a-b);
console.log(arr)
arr.sort((a,b)=>b-a);
console.log(arr)

var num=111;
var a=num.toString(2), 
    b=num.toString(8), 
    c=num.toString(16), 
console.log([a,b,c])

var arr=[[1,2],[3,4],[5,6]];
var result=[].concat(...arr);
console.log(result); 

function repeat(s,n){
  return [...Array(n+1)].join(s);
}
console.log(repeat("a",5));
console.log(repeat("abc",5));

var str="Hello World!";
console.log(str.indexOf("e"))
console.log(str.lastIndexOf("e"))
console.log(str.search("e"))

var str="Hello World!";
console.log(str.indexOf("o"))
console.log(str.lastIndexOf("o"))
console.log(str.search("o"))

var str="Hello World!";
console.log(str.indexOf("o",5))
console.log(str.lastIndexOf("o",5))
console.log(str.search("o"))

var arr=[1,2,3,4,5,6,100,999]
arr.sort((a,b)=>{
  if (a%2==b%2) return a-b;
  if (a%2>b%2) return -1;
  return 1;
})
console.log(arr)

var a=[1,2,3,4,5];
console.log(a.every(x=>x>0));                             
console.log(a.every(x=>x>1)); 

❓Что будет на выходе?

var a=[1,2,3,4,5];
a.every(x=>{
  console.log(x); 
  return x<4;
})

var str="             abc                ";
console.log(str.trim());
str="\n\n\n\nabc\t\t\t"
console.log(str.trim());

function plus(a,b){
  console.log(`${a} + ${b} = ${a+b}`);
}
plus(1,2);
plus(3,4);

function repeatIt(s){
  console.log(`${s} ${s} ${s}`);
}
repeatIt `a`;
repeatIt `ab`;

var num=111;
var a=num.toFixed(), 
    b=num.toExponential(), 
    c=num.toPrecision()
console.log([a,b,c])

var num=111;
var a=num.toFixed(), 
    b=num.toExponential(), 
    c=num.toPrecision()
console.log([a,b,c])