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書名： Ext JS 3.0 Cookbook
作者名： Jorge Ramon
本章字數： 320字
更新時間： 2021-04-01 13:43:44

Determining the object type and converting empty references to a default value

This recipe teaches you how to determine the types of different objects using the facilities of Ext JS, as well as a simple method that can be used to initialize empty references with a default value.

How to do it...

You can determine the types of different objects in the following way:

Create some dummy data structures:

var colorsArray = new Array();
colorsArray[0] = 'Blue';
colorsArray[1] = 'Red';
colorsArray[2] = 'White';
var colorsObject = { color1: 'Blue', color2: 'Red', color3: 'White' };
var aNumber = 1;
var aString = '1';
var sample;
var empty;

Check the types of our variables:

var colorsArrayType = Ext.type(colorsArray);
// colorsArrayType's value is "array".
var isArray = Ext.isArray(colorsArray);
// isArray is true
var colorsObjectType = Ext.type(colorsObject);
// colorsObjectType's value is "object".
var isArray = Ext.isArray(colorsObject);
// isArray is false
var number = Ext.num(aNumber, 0);
// number is 1.
number = Ext.num(aString, 0);
// Since aString is not numeric, the supplied
// default value (0) will be returned.
var defined = Ext.util.Format.undef(sample);
// defined is an empty string
sample = "sample is now defined";
defined = Ext.util.Format.undef(sample);
// defined is now "sample is now defined".
var notEmpty = Ext.value(empty, 'defaultValue', false);
// notEmpty is 'defaultValue'

How it works...

The Ext.type(object) function is capable of detecting elements, objects, text nodes, whitespaces, functions, arrays, regular expressions, numbers, and node lists.

As its name indicates, Ext.isArray(object) simply checks whether the passed object is a JavaScript array. Ext.num(value, defaultValue), in turn, does a numeric type check on the passed value and returns the default value when the argument is not numeric.

Ext.util.Format.undef(value) is a very useful function when you need to test for undefined values. It returns either the supplied argument or an empty string if the argument is undefined.

Ext.value(value, defaultValue, allowBlank) also allows you to specify a default value when the value being tested is undefined.

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Ext JS 3.0 Cookbook

Determining the object type and converting empty references to a default value

How to do it...

How it works...