es-check

When using polyfills like core-js, es-check might flag modern features as errors. Use these options to manage polyfill detection:

• --checkForPolyfills: Automatically detects common polyfill patterns (e.g., core-js imports or common methods for Array, String, Object, Promise, and RegExp).
• --ignorePolyfillable: Ignores all features that can be polyfilled, or limits the scope to a specific library (e.g., --ignorePolyfillable=core-js).
• --allowList: Explicitly allows specific features regardless of the target ES version.
• --ignore: Completely ignores specific features (use as a temporary measure).

# Automatic detection
es-check es2022 './dist/**/*.js' --checkFeatures --checkForPolyfills

# Explicitly allow specific features
es-check es2022 './dist/**/*.js' --checkFeatures --allowList="ArrayToSorted,ObjectHasOwn"

# Ignore all polyfillable features
es-check es2017 './dist/**/*.js' --checkFeatures --ignorePolyfillable

If ES Check is failing, ensure your build pipeline is correctly transpiling code to the target version.

Webpack

Ensure babel-loader is configured with the correct @babel/preset-env targets (e.g., ie: 11 for ES5):

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: "babel-loader",
          options: {
            presets: [
              [
                "@babel/preset-env",
                {
                  targets: { ie: 11 },
                },
              ],
            ],
          },
        },
      },
    ],
  },
};

Babel

Verify your .babelrc targets:

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "targets": {
          "browsers": ["last 2 versions", "ie >= 11"]
        }
      }
    ]
  ]
}

TypeScript

Ensure your tsconfig.json has the correct target and lib settings:

{
  "compilerOptions": {
    "target": "ES5",
    "lib": ["ES5", "DOM"]
  }
}

// Webpack example
module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: "babel-loader",
          options: {
            presets: [["@babel/preset-env", { targets: { ie: 11 } }]],
          },
        },
      },
    ],
  },
};

How you select files significantly impacts performance.

• Use specific patterns: Targeting specific directories is more efficient than broad wildcards.
• Avoid overly broad globs: Using patterns like './**/*.js' with --not='node_modules' is less efficient than explicitly defining the directories to include.
• Check bundled files: Running es-check on a single large bundle is faster than running it on many small individual source files.
• Pre-filter with shell commands: For complex exclusions, use tools like find to pass a specific list of files to es-check via xargs.

# Good - specific patterns
es-check es5 './dist/**/*.js' './lib/**/*.js'

# Less efficient - overly broad
es-check es5 './**/*.js' --not='node_modules'

# Faster - one large file
es-check es5 './dist/bundle.min.js'

# Pre-filtering with shell
find ./dist -name "*.js" -not -path "*/vendor/*" | xargs es-check es5

For large projects, you can tune es-check performance using the following settings:

• File Caching: Enabled by default. Disable it using --noCache.
• Batch Processing: Use --batchSize to control how many files are processed in parallel. This helps manage memory usage in constrained environments.

# Process 10 files at a time to save memory
es-check es5 './dist/**/*.js' --batchSize 10