ASSERT is available since version 1.0.
Prototype:
boolean ASSERT(boolean condition[, string szErrorMessage=""])
Parameters
condition
if false, a run time error will be fired
szErrorMessage
the error message text
Description:
Asserts for a condition.
Return value:
Returns true if the condition is true, false otherwise.
Example
...
var a=0, b=5;
ASSERT(a!=0,"Division by 0");
echo b/a;
...