Learning the iOS 4 SDK for JavaScript Programmers

Operators

Your knowledge of JavaScript operators sets you up perfectly for C/Objective-C operators. A few JavaScript operators don’t apply (function(), typeof, void, and delete), but the rest are in play and with the same general precedence rules.

You do need to be cautious when applying your knowledge of JavaScript comparison operators to Objective-C. JavaScript attempts to find common ground in comparing string and numeric values. For example, consider the following JavaScript function:

function comparisonTest() {
    fiveString = "5";
    fiveNumber = 5;
    return fiveString == fiveNumber;
}

Even though the == equality comparison operator compares a number against a string, JavaScript returns true for this function. Only by substituting the strictly equals operator (===) would the value types be taken into account (in which case the function returns false). In Objective-C, such disparate value types would never be considered to be equal. But numeric types are not as strict, so the integer 5 and the float 5.00, for example, are considered equal.

The C language adds typecasting as an operation to take into account when determining how an expression evaluates. Typecasting (e.g., converting a float to an integer by preceding the integer’s value with (float)) has a high precedence, ahead of common arithmetic operators. This allows a value to be cast into the desired type before math operations apply to the value.