13 Noteworthy Points from Google’s JavaScript Style Guide

Don’t use var anymore

Declare all local variables with either const or let. Use const by default, unless a variable needs to be reassigned. The var keyword must not be used.

Arrow functions are preferred

Arrow functions provide a concise syntax and fix a number of difficulties with this. Prefer arrow functions over the function keyword, particularly for nested functions

Use template strings instead of concatenation

Use template strings (delimited with `) over complex string concatenation, particularly if multiple string literals are involved. Template strings may span multiple lines.
// bad
function sayHi(name) {
 return 'How are you, ' + name + '?';
}

// bad
function sayHi(name) {
 return ['How are you, ', name, '?'].join();
}

// bad
function sayHi(name) {
 return `How are you, ${ name }?`;
}

// good
function sayHi(name) {
 return `How are you, ${name}?`;
}
“for… of” is the preferred type of ‘for loop’

With ES6, the language now has three different kinds of for loops. All may be used, though for–of loops should be preferred when possible.

Constants should be named in ALL_UPPERCASE separated by underscores

Constant names use CONSTANT_CASE: all uppercase letters, with words separated by underscores.