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This article covers features introduced in SpiderMonkey 1.8

Convert a JavaScript string to a C string.


char *
JS_EncodeString(JSContext *cx, JSString *str);

char *
JS_EncodeStringToUTF8(JSContext *cx, JS::HandleString str); // Added in SpiderMonkey 24
Name Type Description
cx JSContext * A context. Requires request. In a JS_THREADSAFE build, the caller must be in a request on this JSContext..
str JSString * / JS::HandleString A string to encode.


JS_EncodeString and JS_EncodeStringToUTF8 convert the specified JavaScript str to a C string (an array of 8-bit chars).

If JS_CStringsAreUTF8 is true, then the returned string of JS_EncodeString is UTF-8, and the conversion is lossless. Otherwise the high byte is simply dropped from each char16_t.

JS_EncodeStringToUTF8 encode the string to UTF-8.

The array returned by JS_EncodeString on success is allocated as though by a call to JS_malloc. The caller may modify it and is responsible for freeing it.

Note that for non-ASCII strings, if JS_CStringsAreUTF8 is false, these functions can return a corrupted copy of the contents of the string. Use JS_GetStringChars to access the 16-bit characters of a JavaScript string without conversions or copying.

On success, JS_EncodeString and JS_EncodeStringToUTF8 return a pointer to the char array, which is null-terminated.

On failure, JS_EncodeString and JS_EncodeStringToUTF8 return NULL

See Also

Document Tags and Contributors

 Contributors to this page: kscarfone, arai
 Last updated by: kscarfone,