diff --git a/README.md b/README.md
index 98e9039..40af623 100644
--- a/README.md
+++ b/README.md
@@ -12,18 +12,28 @@ Operating on the NODE_ENV environmental variable
 
 ## Usage
 
+### Install
+
+```shell
+npm install node-env-manager
+```
+
 ### CONST
 
 ```javascript
 const { ENV } = require("node-env-manager");
 
-ENV.PROD  // -> "production"
-ENV.DEV   // -> "development"
-ENV.LOCAL // -> "local"
-ENV.TEST  // -> "test"
-ENV.EXP   // -> "experience"
-ENV.GRAY  // -> "gray"
-ENV.CI    // -> "ci"
+ENV.PROD          // -> "production",
+ENV.PRODUCTION    // -> "production",
+ENV.DEV           // -> "dev",
+ENV.DEVELOP       // -> "develop",
+ENV.DEVELOPMENT   // -> "development",
+ENV.LOCAL         // -> "local",
+ENV.TEST          // -> "test",
+ENV.EXP           // -> "exp",
+ENV.EXPERIENCE    // -> "experience",
+ENV.GRAY          // -> "gray",
+ENV.CI            // -> "ci"
 ```
 
 ### Mothods
@@ -31,7 +41,7 @@ ENV.CI    // -> "ci"
 ```javascript
 const env = require("node-env-manager");
 
-env.init(); // set `process.env.NODE_ENV` value if this is null
+env.init(); // set `process.env.NODE_ENV` value if the value is null
 env.set();  // set `process.env.NODE_ENV` value
 env.get();  // get `process.env.NODE_ENV` value
 
diff --git a/lib/index.ts b/lib/index.ts
index fbabca2..7fe113f 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -2,14 +2,22 @@
 export enum ENV {
     /** 开发环境 */
     PROD = "production",
+    /** 开发环境 */
+    PRODUCTION = "production",
+    /** 生产环境 */
+    DEV = "dev",
+    /** 生产环境 */
+    DEVELOP = "develop",
     /** 生产环境 */
-    DEV = "development",
+    DEVELOPMENT = "development",
     /** 本地环境 */
     LOCAL = "local",
     /** 测试环境 */
     TEST = "test",
     /** 正式环境 */
-    EXP = "experience",
+    EXP = "exp",
+    /** 正式环境 */
+    EXPERIENCE = "experience",
     /** 灰度环境 */
     GRAY = "gray",
     /** CI 环境 */
@@ -36,7 +44,7 @@ export const get = () => {
  * @param env {string}
  */
 export const set = (env: ENV | string) => {
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
     env = env.trim().toLowerCase();
@@ -50,11 +58,12 @@ export const set = (env: ENV | string) => {
  */
 export const isLocal = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return ["local"].map((item) => item.trim().toUpperCase()).indexOf(env) !== -1;
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.LOCAL ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -63,11 +72,12 @@ export const isLocal = () => {
  */
 export const isTest = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return ["test"].map((item) => item.trim().toUpperCase()).indexOf(env) !== -1;
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.TEST ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -76,15 +86,12 @@ export const isTest = () => {
  */
 export const isDev = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return (
-        ["dev", "develop", "development"]
-            .map((item) => item.trim().toUpperCase())
-            .indexOf(env) !== -1
-    );
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.DEV, ENV.DEVELOP, ENV.DEVELOPMENT ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -93,15 +100,12 @@ export const isDev = () => {
  */
 export const isProd = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return (
-        ["prod", "production"]
-            .map((item) => item.trim().toUpperCase())
-            .indexOf(env) !== -1
-    );
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.PROD, ENV.PRODUCTION ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -110,15 +114,12 @@ export const isProd = () => {
  */
 export const isExp = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return (
-        ["exp", "experience"]
-            .map((item) => item.trim().toUpperCase())
-            .indexOf(env) !== -1
-    );
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.EXP, ENV.EXPERIENCE ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -127,11 +128,12 @@ export const isExp = () => {
  */
 export const isGray = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return ["gray"].map((item) => item.trim().toUpperCase()).indexOf(env) !== -1;
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.GRAY ];
+    return envs.indexOf(env) !== -1;
 };
 
 /**
@@ -140,9 +142,10 @@ export const isGray = () => {
  */
 export const isCI = () => {
     let env = process.env.NODE_ENV;
-    if (typeof env !== "string") {
+    if (!env || typeof env !== "string") {
         return false;
     }
-    env = env.trim().toUpperCase();
-    return ["ci"].map((item) => item.trim().toUpperCase()).indexOf(env) !== -1;
+    env = env.trim().toLowerCase();
+    const envs: string[] = [ ENV.CI ];
+    return envs.indexOf(env) !== -1;
 };
diff --git a/package.json b/package.json
index 2a4658c..6d6e5d3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "node-env-manager",
-  "version": "1.0.0",
+  "version": "1.0.1",
   "description": "Operating on the NODE_ENV environmental variable",
   "main": "dist/index.js",
   "types": "lib/index.ts",
@@ -23,6 +23,8 @@
     "environment",
     "env",
     "nodeenv",
+    "node-env",
+    "node_env",
     "NODE_ENV",
     "test",
     "local",
diff --git a/test/is.spec.ts b/test/is.spec.ts
index 0bdc1a8..8aed6a7 100644
--- a/test/is.spec.ts
+++ b/test/is.spec.ts
@@ -5,64 +5,65 @@ test.beforeEach(() => {
     delete process.env.NODE_ENV;
 });
 
-test((t) => {
+test("isProd", (t) => {
     process.env.NODE_ENV = env.ENV.PROD;
     t.true(env.isProd());
 });
 
-test((t) => {
+test("isProd", (t) => {
     t.false(env.isProd());
 });
 
-test((t) => {
+test("isDev", (t) => {
     process.env.NODE_ENV = env.ENV.DEV;
     t.true(env.isDev());
 });
-test((t) => {
+
+test("isDev", (t) => {
     t.false(env.isDev());
 });
 
-test((t) => {
+test("isLocal", (t) => {
     process.env.NODE_ENV = env.ENV.LOCAL;
     t.true(env.isLocal());
 });
 
-test((t) => {
+test("isLocal", (t) => {
     t.false(env.isLocal());
 });
 
-test((t) => {
+test("isTest", (t) => {
     process.env.NODE_ENV = env.ENV.TEST;
     t.true(env.isTest());
 });
 
-test((t) => {
+test("isTest", (t) => {
     t.false(env.isTest());
 });
 
-test((t) => {
+test("isExp", (t) => {
     process.env.NODE_ENV = env.ENV.EXP;
     t.true(env.isExp());
 });
 
-test((t) => {
+test("isExp", (t) => {
     t.false(env.isExp());
 });
 
-test((t) => {
+test("isGray", (t) => {
     process.env.NODE_ENV = env.ENV.GRAY;
     t.true(env.isGray());
 });
 
-test((t) => {
+test("isGray", (t) => {
     t.false(env.isGray());
 });
 
-test((t) => {
+test("isCI", (t) => {
     process.env.NODE_ENV = env.ENV.CI;
     t.true(env.isCI());
 });
 
-test((t) => {
+test("isCI", (t) => {
     t.false(env.isCI());
 });
diff --git a/test/set.spec.ts b/test/set.spec.ts
index ee8d631..68aee66 100644
--- a/test/set.spec.ts
+++ b/test/set.spec.ts
@@ -9,3 +9,14 @@ test((t) => {
     t.true(env.set(env.ENV.DEV));
     t.true(env.isDev());
 });
+
+test((t) => {
+    t.false(env.set(1 as any));
+});
+
+test((t) => {
+    env.init();
+    t.true(env.isDev());
+    t.false(env.set(undefined as any));
+    t.true(env.isDev());
+});