Variables, functions and types should always be used after they've been defined. This issue will flag any code snippets that use variables or types before definition.

Sometimes, the code will run just fine even when the variable is declared after use. Consider the following example:

const ram: Resource = { type: "memory", limit: 1024 ** 3 }
type Resource = {
  type: string;
  limit: number;
}

Here, Resource is used in the annotation before it has been defined. Similarly, it is possible to hoist function declarations and variables declared with the var keyword:

const four = twice(2);
function twice(n: number) {
  return n * 2;
}

However, it makes the code harder to follow when variables or types are declared after being used.

Bad Practice

const knight: Radiant = {
  order: "SurgeBinder"
  strength: 30
}

interface Radiant {
  order: string;
  strength: number;
}

Recommended

interface Radiant {
  order: string;
  strength: number;
}

const knight: Radiant = {
  order: "SurgeBinder"
  strength: 30
}