early-exit.md

Pattern: Missing early exit

Issue: -

Description

Recommends to use an early exit instead of a long if block. This means to return early from a function, continue early in loop, or break early in a switch case.

So instead of:

function f() {
  if (so) {
    lots;
    of;
    code;
  }
}

Prefer:

function f() {
  if (!so) return;
  lots;
  of;
  code;
}

This rule also warns for if-else blocks where one branch is large and the other is a single line. So instead of:

for (const x of xs) {
  if (so) {
    simple;
  } else {
    lots;
    of;
    code;
  }
}

Prefer:

for (const x of xs) {
  if (so) {
    simple;
    continue;
  }

  lots;
  of;
  code;
}

An options object as in "early-exit": [true, { "max-length": 4, "ignore-constructor": true }] may be provided.

"max-length" configures what makes a block count as "large". The default is 2 lines.

If you set "max-length" to 0, the rule will always suggest an early return, regardless of the line count. For example:

// instead of
function f() {
  if (so) {
    singleLine();
  }
}
// prefer
function f() {
  if (!so) return;
  singleLine();
}

// and instead of
for (const x of xs) {
  if (so) {
    foo();
  } else {
    bar();
  }
}
// prefer
for (const x of xs) {
  if (so) {
    foo();
    continue;
  }
  bar();
}

In addition you can choose to ignore if statements within class constructors with "ignore-constructor": true which defaults to false. Enabling this option prevents potential mistakes by overriding the constructed object with a non-primitive return value.

Further Reading

• TSLint - early-exit