1. Arrow functions in ES6

In Javascript ES6 you can write a function like const myFunction = (x) => { return x + 1; } but you can also write it like const myFunction = x => x + 1;

2. Copying an array

If you are copying an array like this const newArray = myArray; is time to stop doing that and do it like this const newArray = [...myArray];. This way it will deep copy the whole array

3. Tagged template literals

Does this look familiar?
const name = "Andy";
alert("Hello " + name + " !");

You can avoid doing that like this:
const name = "Andy";
`Hello ${name} !`;

5. Check if a string contains a substring

Until recently if you wanted to check if a string contains a substring, you would do string.indexOf(substring) > -1 but in ES6 we now can do it like string.includes(substring)