Got it, let's break down your problem and fix it step by step.

The root issue here is that Visual Studio 2015's native JavaScript language service has limited support for ES6+ features—function default parameters (like pipeId = undefined in your code var _BindAddNewPipelineButton = function(pipeId = undefined, enableEditMode = false) {) are an ES6 syntax, which is why it's throwing errors and messing up syntax highlighting. Here's what you can do to resolve this:

1. Install Extensions for Enhanced ES6 Support #

These extensions will add proper ES6 syntax highlighting, intellisense, and error checking to VS 2015:

• Web Essentials 2015: This is a widely-used extension that boosts VS's handling of modern web languages. It fully supports ES6 syntax for JavaScript, fixing both highlighting and error issues. To install it, go to Tools > Extensions and Updates > Online and search for "Web Essentials 2015".
• TypeScript Tools for Visual Studio 2015: Even if you're not writing TypeScript, this extension updates VS's underlying language service to better recognize ES6 JavaScript features. It's a reliable workaround for gaps in native JS support.
• ESLint Extension: If you want stricter syntax validation alongside ES6 support, configure this extension to use ES6 rules—it will automatically fix the highlighting and error reporting for your default parameter code.

2. Configure Your Project to Use ES6 Standards #

Create a jsconfig.json file in your project's root directory with the following content:

{
  "compilerOptions": {
    "target": "ES6"
  },
  "exclude": [
    "node_modules",
    "bower_components"
  ]
}

This file tells Visual Studio to parse your JavaScript files using ES6 standards, which should resolve the syntax errors and highlighting glitches caused by the default parameter syntax.

3. Resolve the Missing JavaScript Language Service Issue #

If you can't locate the JavaScript Language Service in VS 2015, try these steps:

• Update to Visual Studio 2015 Update 3: Microsoft released this update with improved JavaScript/ES6 support. Installing it may restore or update the missing language service component.
• Repair Your Visual Studio Installation: Go to Control Panel > Programs > Programs and Features, find Visual Studio 2015, select Change > Repair. This ensures all required components (including the JavaScript Language Service) are installed correctly.
• Check for Disabled Components: In VS, navigate to Tools > Options > Text Editor > JavaScript/TypeScript > Language Service. If this section is missing entirely, a repair is the most likely fix to restore the component.

内容的提问来源于stack exchange，提问作者ankur