if-statements allow multiple arguments and don't check for constant conditions after the first argument

🔎 Search Terms

"if statement", "constant condition"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about common bugs

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBBIFsCmBhAFk4BrAlmA5gGICuYwUO4MAvDABQAOAhgE5MICMAXHFC3vgA0MZmwQAmHtH4FhIBhXBMANgAVW7AMw0YfYkgCUNAHwwA3gCgY1mAHpbMACYhexAGZurNlkijEWYLos+gDcFgC+Fhb2MCoA7kwAnhAwbioQSMI+EMTKsCBucIioGNgCJGSKgfFJKTj4YCA+jhY4bnTwyOiYuAQV5JRgdABEouwcw8KjGhLDBsJpyhlGljYwEVExjkgMSGDbYPmB2bn5hZ0lPeWkA+Ct7RfdZX03VSNjnJMw02LiX4vLFZeawRIA

💻 Code

const someCheckingFunction = (param1: string, param2: string, optionalParam3 = true) => {
    // do stuff
    return true;
}

// always false, result of someCheckingFunction always ignored
if(someCheckingFunction("param1", "param2"), false) {
    
}

// dependent on result of someCheckingFunction
if(someCheckingFunction("param1", "param2", false)) {
    
}

🙁 Actual behavior

Due to a mistake in my bracket placement as seen in the example, I accidentally learned that multiple arguments in an if statement are possible.

Currently that means:

1. only the last argument is used for the if statement check
2. even for constant conditions there is not error visible

🙂 Expected behavior

What I would expect:

1. don't allow multiple arguments, this only happens because someone made an error
2. at least show an error if there is a constant condition

Additional information about the issue

No response

Reproduce the provided example in the linked TypeScript Playground and compare the two if-statement forms described in the report. Review the compiler behavior for comma-separated expressions and constant conditions; done means the intended diagnostics or accepted behavior are defined and covered for these examples.