>> ({ define: typeof define === "function"
>> ? define // browser
>> : function(F) { F(require,exports,module) } }). // Node.js
>> define(function (require, exports, module) {
>> // Node.js module code goes here
>> });
> Sure, but in that case the test
> typeof define === 'function'
> tests the value that the variable 'define' references. It does not test if
> "define' has been declared.
I’m not completely sure I understand what you mean.
typeof define === "function"
- Node.js: variable "define" has not been declared. Because of that, typeof
define is "undefined" and the expression is false.
- Browser + RequireJS: There is a global variable "define" whose value is a
function. Hence typeof define is "function" and the expression is true.
> The exists operator would work as follows (slightly edited from a previous
> email):
>
> console.log(exists globalUnknown); // false
>
> // undefined and null in several variations
>
> var myvar;
> console.log(exists myvar); // false
>
> Well myvar is declared so how can exists be false?
Right. Maybe the operator should have a different name. "isDefined"? "has a
value" expressed as an operator name?
isDefined x
would be syntactic sugar for
typeof x !== "undefined" && x !== null
The expression would not throw an exception if x hasn’t been declared.
The two most important use cases for typeof probably are:
- isDefined
- Helping to implement getTypeName() whose results are
- "null", "undefined", "boolean", "number", "string" for primitive values
- [[Class]] for objects ("String", "Date", etc.)
--
Dr. Axel Rauschmayer
a...@rauschma.de
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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