perf: Improve performance

index.js

@@ -4,7 +4,7 @@ const { format } = require('util')
 
 function build () {
   const codes = {}
-  const emitted = new Map()
+  const emitted = new Set()
 
   function create (name, code, message) {
     if (!name) throw new Error('Warning name must not be empty')
@@ -37,16 +37,15 @@ function build () {
       }
     }
 
-    emitted.set(code, false)
     codes[code] = buildWarnOpts
 
     return codes[code]
   }
 
   function emit (code, a, b, c) {
     if (codes[code] === undefined) throw new Error(`The code '${code}' does not exist`)
-    if (emitted.get(code) === true) return
-    emitted.set(code, true)
+    if (emitted.has(code)) return
+    emitted.add(code)
 
     const warning = codes[code](a, b, c)
     process.emitWarning(warning.message, warning.name, warning.code)

test/emit-interpolated-string.test.js

@@ -12,7 +12,7 @@ test('emit with interpolated string', t => {
     t.equal(warning.name, 'FastifyDeprecation')
     t.equal(warning.code, 'CODE')
     t.equal(warning.message, 'Hello world')
-    t.ok(emitted.get('CODE'))
+    t.ok(emitted.has('CODE'))
   }
 
   create('FastifyDeprecation', 'CODE', 'Hello %s')

test/emit-once-only.test.js

@@ -13,7 +13,7 @@ test('emit should emit a given code only once', t => {
     t.equal(warning.name, 'FastifyDeprecation')
     t.equal(warning.code, 'CODE')
     t.equal(warning.message, 'Hello world')
-    t.ok(emitted.get('CODE'))
+    t.ok(emitted.has('CODE'))
   }
 
   create('FastifyDeprecation', 'CODE', 'Hello world')

test/jest.test.js

@@ -14,7 +14,7 @@ test('works with jest', done => {
   // we can only test it was emitted indirectly
   // and test no exception is raised
   setImmediate(() => {
-    expect(emitted.get('CODE')).toBeTruthy()
+    expect(emitted.has('CODE')).toBeTruthy()
     done()
   })
 })