improve object iteration

modules/assignStyle.ts

@@ -17,23 +17,28 @@ export default function assignStyle(
   for (let i = 0, len = extendingStyles.length; i < len; ++i) {
     const style = extendingStyles[i]
 
-    for (const property in style) {
+    const keys = Object.keys(style)
+    for (let j = 0, len2 = keys.length; j < len2; j++) {
+      const property = keys[j]
       const value = style[property]
       const baseValue = base[property]
 
       if (baseValue && value) {
         if (Array.isArray(baseValue)) {
           base[property] = filterUniqueArray(baseValue.concat(value))
+          // eslint-disable-next-line no-continue
           continue
         }
 
         if (Array.isArray(value)) {
           base[property] = filterUniqueArray([baseValue, ...value])
+          // eslint-disable-next-line no-continue
           continue
         }
 
         if (typeof value === 'object') {
           base[property] = assignStyle({}, baseValue as StyleObject, value)
+          // eslint-disable-next-line no-continue
           continue
         }
       }

modules/camelCaseProperty.ts

@@ -2,7 +2,7 @@ type CacheObject = {
   [key: string]: string
 }
 
-const CSS_VARIABLE = /^--/;
+const CSS_VARIABLE = /^--/
 const DASH = /-([a-z])/g
 const MS = /^Ms/g
 const cache: CacheObject = {}

modules/cssifyObject.ts

@@ -11,19 +11,21 @@ export type StyleObject = {
 export default function cssifyObject(style: StyleObject) {
   let css = ''
 
-  for (const property in style) {
+  const keys = Object.keys(style)
+  for (let i = 0, len = keys.length; i < len; i++) {
+    const property = keys[i]
     const value = style[property]
     if (typeof value !== 'string' && typeof value !== 'number') {
-      continue
-    }
+      // do nothing
+    } else {
+      // prevents the semicolon after
+      // the last rule declaration
+      if (css) {
+        css += ';'
+      }
 
-    // prevents the semicolon after
-    // the last rule declaration
-    if (css) {
-      css += ';'
+      css += cssifyDeclaration(property, value)
     }
-
-    css += cssifyDeclaration(property, value)
   }
 
   return css

package.json

@@ -56,7 +56,7 @@
     "eslint": "^6.8.0",
     "eslint-config-airbnb-base": "^14.1.0",
     "eslint-plugin-import": "^2.20.2",
-    "jest": "^25.2.6",
+    "jest": "^29.7.0",
     "prettier": "^1.7.4",
     "rimraf": "^2.6.1",
     "typescript": "^3.8.3"