Control flow statements

Control flow statements spanning multiple lines always use blocks for the containing code.

for (let i = 0; i < x; i++) {
  doSomething(i);
  andMore();
}


// good
if (x) {
  doSomethingWithALongMethodName(x);
}


// bad
if (x) doSomethingWithALongMethodName(x);

The exception is that if statements fitting on one line may elide the block; If it respects the line length rule, it can get away with emitting the block.

if (x) x.doFoo();

All switch statements must contain a default statement group, even if it contains no code.

switch (x) {
  case Y:
    doSomething();
    break;
  default:
  // nothing to do.
}

Non-empty statement groups (case ...) shall not fall through; gets to execute the code in the next case.

switch (x) {
  case X:
    doSomething();
  // falling through not allowed!
  case Y:
  // ...
}

Empty statement groups are allowed to fall through

switch (x) {
  case X:
  case Y:
    doSomething();
    break;
  default: // nothing to do.
}

Equality Checks

Always use triple equals (=== and the likes !==) , and not double equality (==) operators, in order to avoid type coercion bugs/errors. With the exception of comparisons to the literal null value, which may use the == and != operators to cover both null and undefined values.

// bad
if (foo == 'bar' || x != y) {
  // Hard to understand behaviour due to type coercion.
}


// good
if (foo === 'bar' || x !== y) {
  // All good here.
}


// good
if (x == null) {
  // Will trigger when x is null or undefined.
}