EXIST
NAME
exist - Check if an element exist in a context.
SYNOPSIS
exist (context, element[, strict : bool ]);
DESCRIPTION
This function is used to check if a key (element) exist in a context
PARAMETERS
- context
- Specifies the context
-
- element
- Specifies the key
-
- strict
- This parameter has been implemented in version 5.177. Default for strict is true. If the value is false then:
1. exist will return false on undefined value
2. exist will return false if context is not a context
RETURN
- A boolean set to tru if element is a key in the context
EXAMPLES
Function `exist` may not give results you might expect. Here is a simple case scenario
user = {"name": "Patrick"};
user.uid;"<br>"; // This line will create a key `uid` inside the `user` context, set as undefined.
user;"<br>"; // You may be confused by the fact that when printing the `user` context, the key `uid` does not appear. Since it does not appear, you may think that the key was indeed not created.
user.exist("uid");"<br>"; // ...but `exist` still reveals its existance.
user.uid == undefined;"<br>"; // Testing directly the key `uid` to undefined, will reveal the true existence of the key.
Output result:
{"name":"Patrick"}
true
true
You may want to test the existance of an attribute but disregard the keys set to `undefined`. To do this, use `strict: false
user.exist("uid", strict: false);
Output result:
false
Other examples
assoc = { "x" : 1, "y" : 2 };
assoc.exist("x"); // return true
assoc.exist("a"); // return false
exist(assoc, "y"); //return true;
v = { "x" : 1, "z" : undefined };
exist(v, "x"); // return true
exist(v, "y"); // return false
exist(v, "z"); // return true
exist(v, "x", strict:false); // return true
exist(v, "y", strict:false); // return false
exist(v, "z", strict:false); // return false
v = { "x" : 1 };
v.user = (exist(v, "user"))?"11":"22";
v.user; // return 11
v = { "x" : 1 };
v.user = (exist(strict:false, v, "user"))?"11":"22";
v.user; // return 22
SEE ALSO
AUTHOR
Written by Pierre Laplante and Caroline Laplante, <laplante@sednove.com>
MODIFICATIONS
1.0 2014-09-09 21:24:14 laplante@sednove.com
1.1 2022-04-08 laplante@sednove.com add strict mode
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