JS_GetStringChars
syntax jschar * js_getstringchars(jsstring *str); // obsolete since jsapi 1.8.5 const jschar * js_getstringcharsz(jscontext *cx, jsstring *str); // added in spidermonkey 1.8.2, obsolete since jsapi 33 name type description cx jscontext * (in js_getstringcharsz only) a context.
...(eventually, str becomes unreachable, the garbage collector collects it, and the array is freed by the system.) js_getstringcharsz is the same except that it always returns either a null-terminated string or null, indicating out-of-memory.
... see also bug 609440 - removed js_getstringchars bug 1037869 - removed js_getstringcharsz ...

SpiderMonkey 1.8.5
ngchars js_getgcparameter js_getgcparameterforthread js_getglobalforscopechain js_getinternedstringchars js_getinternedstringcharsandlength js_getownpropertydescriptor js_getpropertyattrsgetterandsetterbyid js_getpropertybyid js_getpropertybyiddefault js_getpropertydefault js_getpropertydescriptorbyid js_getruntimesecuritycallbacks js_getsecuritycallbacks js_getstringcharsandlength js_getstringcharsz js_getstringcharszandlength js_getstringencodinglength js_haspropertybyid js_initctypesclass js_internjsstring js_isconstructing_possiblywithgiventhisobject js_isextensible js_isinrequest js_leavecrosscompartmentcall js_lookuppropertybyid js_lookuppropertywithflagsbyid js_new js_newcompartmentandglobalobject js_newdateobject js_newdateobjectmsec js_newfunctionbyid body new c++ h...
...additionally, js_newstring, js_getstringbytes, and js_getstringchars were removed, replaced by fallible interfaces like js_getstringcharszandlength and js_encodestringtobuffer (not an exhaustive list).

SpiderMonkey 1.8.7
ngchars js_getgcparameter js_getgcparameterforthread js_getglobalforscopechain js_getinternedstringchars js_getinternedstringcharsandlength js_getownpropertydescriptor js_getpropertyattrsgetterandsetterbyid js_getpropertybyid js_getpropertybyiddefault js_getpropertydefault js_getpropertydescriptorbyid js_getruntimesecuritycallbacks js_getsecuritycallbacks js_getstringcharsandlength js_getstringcharsz js_getstringcharszandlength js_getstringencodinglength js_haspropertybyid js_initctypesclass js_internjsstring js_isconstructing_possiblywithgiventhisobject js_isextensible js_isinrequest js_leavecrosscompartmentcall js_lookuppropertybyid js_lookuppropertywithflagsbyid js_new js_newcompartmentandglobalobject js_newdateobject js_newdateobjectmsec js_newfunctionbyid body new c++ h...
...additionally, js_newstring, js_getstringbytes, and js_getstringchars were removed, replaced by fallible interfaces like js_getstringcharszandlength and js_encodestringtobuffer (not an exhaustive list).

JS_MakeStringImmutable
(when an application shares a string by storing it in a javascript object that another thread can read, the javascript engine automatically makes the string thread-safe.) after a successful call to js_makestringimmutable, subsequent calls to js_getstringcharsz on the same string are guaranteed to succeed, and subsequent calls to js_getstringchars on the same string are guaranteed to return a null-terminated string.

JSAPI reference
flat added in spidermonkey 38 js_assert_string_is_flat added in spidermonkey 1.8.5 js_flattenstring added in spidermonkey 1.8.5 typedef jschar obsolete since jsapi 35 js_newstring obsolete since jsapi 1.8.5 js_newgrowablestring obsolete since jsapi 27 js_getstringbytes obsolete since jsapi 1.8.5 js_getstringbytesz obsolete since jsapi 1.8.5 js_getstringchars obsolete since jsapi 1.8.5 js_getstringcharsz obsolete since jsapi 33 js_getstringcharsandlength added in jsapi 1.8.5 obsolete since jsapi 33 js_getstringcharsz added in spidermonkey 1.8.5 obsolete since jsapi 33 js_getstringcharszandlength added in spidermonkey 1.8.5 obsolete since jsapi 33 js_getflatstringchars obsolete since jsapi 33 js_makestringimmutable obsolete since javascript 1.8.5 js_encodecharacters obsolete since jsapi 19 ...

SpiderMonkey 38
nt32 (bug 1112774) js_doubletouint32 (bug 1112774) js_enumeratestub (bug 1103152) js_evaluatescript (bug 1100579) js_evaluateucscript (bug 1100579) js_executescriptversion (bug 1095660) js_getflatstringchars (bug 1037869) js_getfunctioncallback (bug 1103269) js_getinternedstringchars (bug 1037869) js_getinternedstringcharsandlength (bug 1037869) js_getstringcharsandlength (bug 1037869) js_getstringcharsz (bug 1037869) js_getstringcharszandlength (bug 1037869) js_gettypename (bug 1037718) js_isabouttobefinalized (bug 650161) js_lookupelement (bug 1094176) js_lookupproperty (bug 1094176) js_lookuppropertybyid (bug 1094176) js_lookupucproperty (bug 1094176) js_newpropertyiterator (bug 1081660) js_nextproperty (bug 1081660) js_resolvestub (bug 1103152) js_setfinalizecallback (bug 996785) ...