[javascript] How to loop through a plain JavaScript object with the objects as members?

In ES6/2015 you can loop through an object like this: (using arrow function)

Object.keys(myObj).forEach(key => {
  console.log(key);        // the name of the current key.
  console.log(myObj[key]); // the value of the current key.
});

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In ES7/2016 you can use Object.entries instead of Object.keys and loop through an object like this:

Object.entries(myObj).forEach(([key, val]) => {
  console.log(key); // the name of the current key.
  console.log(val); // the value of the current key.
});

The above would also work as a one-liner:

Object.entries(myObj).forEach(([key, val]) => console.log(key, val));

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In case you want to loop through nested objects as well, you can use a recursive function (ES6):

const loopNestedObj = obj => {
  Object.keys(obj).forEach(key => {
    if (obj[key] && typeof obj[key] === "object") loopNestedObj(obj[key]); // recurse.
    else console.log(key, obj[key]); // or do something with key and val.
  });
};

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Same as function above, but with ES7 Object.entries() instead of Object.keys():

const loopNestedObj = obj => {
  Object.entries(obj).forEach(([key, val]) => {
    if (val && typeof val === "object") loopNestedObj(val); // recurse.
    else console.log(key, val); // or do something with key and val.
  });
};

Here we loop through nested objects change values and return a new object in one go using Object.entries() combined with Object.fromEntries() (ES10/2019):

const loopNestedObj = obj =>
  Object.fromEntries(
    Object.entries(obj).map(([key, val]) => {
      if (val && typeof val === "object") [key, loopNestedObj(val)]; // recurse
      else [key, updateMyVal(val)]; // or do something with key and val.
    })
  );

Another way of looping through objects is by using for ... in and for ... of. See @vdegenne's nicely written answer.