JS_HasProperty

Determine whether a JavaScript object has a specified property.

Syntax

bool
JS_HasProperty(JSContext *cx, JS::HandleObject obj, const char *name,
               bool *foundp);

bool
JS_HasUCProperty(JSContext *cx, JS::HandleObject obj,
                 const char16_t *name, size_t namelen,
                 bool *vp);

bool
JS_HasPropertyById(JSContext *cx, JS::HandleObject obj, JS::HandleId id,
                   bool *foundp); // Added in SpiderMonkey 1.8.1
Name Type Description
cx JSContext * A context. Requires request. In a JS_THREADSAFE build, the caller must be in a request on this JSContext.
obj JS::HandleObject Object to search on for the property.
name or id const char * or const char16_t or JS::HandleId Name of the property to look up.
namelen size_t (only in JS_HasUCProperty) The length of name in characters, or -1 to indicate that name is null-terminated.
foundp bool * Non-null pointer to a variable of type bool. On success, JS_HasProperty stores true in this variable if obj has a property with the given name, and false if not.

Description

JS_HasProperty searches an object, obj, and its prototype chain, for a property with the specified name. It behaves like the JavaScript expression name in obj. JS_HasUCProperty is the corresponding Unicode API. JS_HasPropertyById is the same but takes a JS::HandleId for the property name.

If the property exists, this function sets *foundp to true and returns true.

If the object obj has no such property, the function sets *foundp to false and returns true (to indicate that no error occurred).

If an error occurs during the search, the function returns false, and the value of *foundp is undefined.

See Also