fix(esbuild): use precise es version target for a runtime

fix #3

Author: floydspace

.gitignore

@@ -4,3 +4,4 @@ node_modules
 dist
 *.log
 package-lock.json
+coverage

src/function.ts

@@ -6,12 +6,12 @@ import { mergeRight, union, without } from 'ramda';
 
 import { packExternalModules } from './pack-externals';
 import { NodejsFunctionProps } from './props';
-import { extractFileName, findProjectRoot, nodeMajorVersion } from './utils';
+import { extractFileName, findProjectRoot, NodeMajorESMap, nodeMajorVersion } from './utils';
 
 const BUILD_FOLDER = '.build';
 const DEFAULT_BUILD_OPTIONS: es.BuildOptions = {
   bundle: true,
-  target: 'es2017',
+  target: NodeMajorESMap[nodeMajorVersion()],
 };
 
 /**
@@ -33,10 +33,10 @@ export class NodejsFunction extends lambda.Function {
     const exclude = union(props.exclude || [], ['aws-sdk']);
     const packager = props.packager ?? true;
     const handler = props.handler ?? 'index.handler';
-    const defaultRunTime = nodeMajorVersion() >= 12
+    const defaultRuntime = nodeMajorVersion() >= 12
       ? lambda.Runtime.NODEJS_12_X
       : lambda.Runtime.NODEJS_10_X;
-    const runtime = props.runtime ?? defaultRunTime;
+    const runtime = props.runtime ?? defaultRuntime;
     const entry = extractFileName(projectRoot, handler);
 
     es.buildSync({

src/props.ts

@@ -50,7 +50,17 @@ export interface NodejsFunctionProps extends lambda.FunctionOptions {
   /**
    * The esbuild bundler specific options.
    *
-   * @default = { bundle: true, target: 'es2017' }
+   * @default = NodeMajorESMap {
+   *   8 : 'es2016'
+   *   9 : 'es2017'
+   *   10: 'es2018'
+   *   11: 'es2018'
+   *   12: 'es2019'
+   *   13: 'es2019'
+   *   14: 'es2020'
+   *   15: 'es2020'
+   * >=16: 'esnext'
+   * };
    */
   readonly esbuildOptions?: BuildOptions;
 }

src/utils.ts

@@ -105,6 +105,18 @@ export function nodeMajorVersion(): number {
   return parseInt(process.versions.node.split('.')[0], 10);
 }
 
+export const NodeMajorESMap = {
+  8: 'es2016',
+  9: 'es2017',
+  10: 'es2018',
+  11: 'es2018',
+  12: 'es2019',
+  13: 'es2019',
+  14: 'es2020',
+  15: 'es2020',
+  16: 'esnext',
+};
+
 /**
  * Returns the package manager currently active if the program is executed
  * through an npm or yarn script like: