Repository: TypeScript
Issue: Include Default Parameter Values in Signature Help 
Labels: Suggestion,Awaiting More Feedback,VS Code Tracked,Domain: Signature Help,Domain: Quick Info

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From https://github.com/Microsoft/vscode/issues/28925

**TypeScript Version:**  2.4.0

**Feature Request**
`signatureHelp` current shows when a parameter is optional but does not include any information about that parameter's default value:


```ts
function foo(x = 10) { }
foo(|)
```


Result of TSServer `signatureHelp`  on `foo`

```
[Trace  - 5:42:22 PM] Response received: signatureHelp (378). Request took 20 ms. Success: true 
Result: {
    "items": [
        {
            "isVariadic": false,
            "prefixDisplayParts": [
                {
                    "text": "foo",
                    "kind": "functionName"
                },
                {
                    "text": "(",
                    "kind": "punctuation"
                }
            ],
            "suffixDisplayParts": [
                {
                    "text": ")",
                    "kind": "punctuation"
                },
                {
                    "text": ":",
                    "kind": "punctuation"
                },
                {
                    "text": " ",
                    "kind": "space"
                },
                {
                    "text": "void",
                    "kind": "keyword"
                }
            ],
            "separatorDisplayParts": [
                {
                    "text": ",",
                    "kind": "punctuation"
                },
                {
                    "text": " ",
                    "kind": "space"
                }
            ],
            "parameters": [
                {
                    "name": "x",
                    "documentation": [],
                    "displayParts": [
                        {
                            "text": "x",
                            "kind": "parameterName"
                        },
                        {
                            "text": "?",
                            "kind": "punctuation"
                        },
                        {
                            "text": ":",
                            "kind": "punctuation"
                        },
                        {
                            "text": " ",
                            "kind": "space"
                        },
                        {
                            "text": "number",
                            "kind": "keyword"
                        }
                    ],
                    "isOptional": true
                }
            ],
            "documentation": [],
            "tags": []
        }
    ],
    "applicableSpan": {
        "start": {
            "line": 3,
            "offset": 5
        },
        "end": {
            "line": 3,
            "offset": 5
        }
    },
    "selectedItemIndex": 0,
    "argumentIndex": 0,
    "argumentCount": 0
}
```

When the default value is a simple literal type, it would be helpful to display this default value in the signature help. This information could be included in the `displayParts` response