User Guide

The C-level API 363
JSBool JS_ExecuteScript()
Description
This function compiles and executes a JavaScript string. If the script generates a return value, it
returns in
*rval.
Arguments
JSContext *cx
, JSObject *obj, char *script, unsigned int sz, jsval *rval
• The cx argument is the opaque JSContext pointer that passes to the JavaScript function.
• The obj argument is a pointer to the object in whose context the script executes. While the
script is running, the
this keyword is equal to this object. Usually this is the JSObject pointer
that passes to the JavaScript function.
• The script argument is a string that contains JavaScript code. If the string size is not specified
(see the
sz argument), the string must be null-terminated.
• The sz argument is the size of the string, in bytes. If sz is 0, the length of the null-terminated
string is computed automatically.
• The rval argument is a pointer to a single jsval structure. The function’s return value is
stored in
*rval.
Returns
A Boolean value: JS_TRUE indicates success; JS_FALSE indicates failure.
JSBool JS_ReportError()
Description
This function describes the reason for a script error. Call this function before returning the value
JS_FALSE for a script error to give the user information about why the script failed (for example,
“wrong number of arguments”).
Arguments
JSContext *cx
, char *error, size_t sz
• The cx argument is the opaque JSContext pointer that passes to the JavaScript function.
• The error argument is a string that contains the error message. The string is copied, so the
caller should free the string when it is not needed. If the string size is not specified (see the
sz
argument), the string must be null-terminated.
• The sz argument is the size of the string, in bytes. If sz is 0, the length of the null-terminated
string is computed automatically.
Returns
A Boolean value: JS_TRUE indicates success; JS_FALSE indicates failure.