Add api: jerry_get_value_without_error_flag (#2096)

It is used to get the reference value from a error value

JerryScript-DCO-1.0-Signed-off-by: Zidong Jiang zidong.jiang@intel.com

docs/02.API-REFERENCE.md

@@ -1486,6 +1486,49 @@ jerry_value_set_error_flag (jerry_value_t *value_p);
 - [jerry_value_t](#jerry_value_t)
 
 
+## jerry_get_value_without_error_flag
+
+**Summary**
+
+If the input value is an error value, then return a new reference to its referenced value.
+Otherwise, return a new reference to the value itself.
+
+*Note*: Returned value must be freed with [jerry_release_value](#jerry_release_value) 
+when it is no longer needed.
+
+**Prototype**
+
+```c
+jerry_value_t 
+jerry_get_value_without_error_flag (jerry_value_t value)
+```
+
+- `value` - api value
+
+**Example**
+
+```c
+{
+  jerry_value_t value;
+  ... // create or acquire value
+  
+  jerry_value_set_error_flag (&value);
+  
+  jerry_value_t real_value = jerry_get_value_without_error_flag (value);
+  ... // process the real_value. Different from `jerry_value_clear_error_flag`, 
+      // the error `value` will not be automatically released after calling 
+      // `jerry_get_value_without_error_flag`.
+
+  jerry_release_value (value);
+  jerry_release_value (real_value);
+}
+```
+
+**See also**
+
+- [jerry_acquire_value](#jerry_acquire_value)
+- [jerry_value_clear_error_flag](#jerry_value_clear_error_flag)
+
 # Getter functions of 'jerry_value_t'
 
 Get raw data from API values.