How to deal with key value pairs in JavaScript object

loops_in_object.js

const test = {a: 1, b: 2, c: 3};

// #1 ES6
for (const [key, value] of Object.entries(test)) {
  console.log(key, value);
}

// #2
for (var k in test){
    if (test.hasOwnProperty(k)) {
         alert("Key is " + k + ", value is " + test[k]);
    }
}

// #3
Object.keys(test).forEach(function (key) {
   // do something with obj[key]
});

// #4
for( var key in test ) {
  var value = test[key];
}

// #5
Object.values(test).forEach(value => ...); // Select value
Object.keys(test).forEach(key => ...); // Select key
Object.entries(test).forEach(([key, value])=> ...); // Select [key, value]