Function js::jsapi::JS_NewDependentString

pub unsafe extern "C" fn JS_NewDependentString(
    cx: *mut JSContext, 
    str: HandleString, 
    start: usize, 
    length: usize
) -> *mut JSString

Create a dependent string, i.e., a string that owns no character storage, but that refers to a slice of another string's chars. Dependent strings are mutable by definition, so the thread safety comments above apply.