Dynamic Selection and traversal of JavaScript objects

(1) dynamic selection methods and attributes

In actual work, we often encounter this situation: call one of the two methods [1] based on a certain condition, or perform read and write operations on one of the two attributes [2. The following code demonstrates this situation:
Copy codeThe Code is as follows:
If (condition ){
MyObj. method1 (someArg );
} Else {
MyObj. method2 (someArg );
}

JavaScript provides a simple syntax, that is, using the square brackets operator ([]) to dynamically select methods and attributes. As shown in the following code, JavaScript has two equivalent member access syntaxes (this feature is common in dynamic languages ):
Obj [expressionResultingInMembername] = obj. memberName

If you used an integer subscript to access an element in the array, you have begun to use the square brackets operator for dynamic member selection. This is because the array object itself contains the attributes (and length attributes) named by the number subscript ). However, JavaScript does not allow you to directly access these attributes using the dot operator (.). Therefore, myArray.0 is invalid in syntax (sorry, this is a cool syntax ).
Why is the square brackets operator more powerful than the dot operator notation? This is because you can use any content in square brackets that represents the member name to access the member of the object. These include literal, variables that store Member names, name combinations (in most cases String concatenation), and condition? ValueIfTrue: valueIfFalse) enables quick if/then selection. All the content will be processed into a string, and JavaScript will use this string to find the corresponding member.
Because functions in JavaScript are also objects, they can be referenced like other values. If the result of an expression is a function, you can call it directly using the brackets operator, just as you call a function directly using the function name.
It should be noted that if you use a lot of such techniques in parameters passed to the method, confusing parentheses may make the code hard to read, in this case, it is more wise to use the regular if/else structure.

(2) JavaScript traversal of Object Attributes and Methods

JavaScript uses the for in statement to traverse object attributes and methods. The for in statement cyclically traverses JavaScript objects. Each loop gets an attribute or method of the object.

Syntax:
Copy codeThe Code is as follows:
For (valueName in ObjectName ){
// Code
}

ValueName is the variable name and stores the name of the attribute or method. The value of valueName changes every cycle.