cval

Description

It's a function to safe get chain value with default value, and avoid 'Cannot read property of undefined' errors.

提供链式调用函数

Useage

	//you can view detail in test/index.js

	var testModel = {
		"a": {
			"b": {
				"c": {
					"d": "valueD"
				}
			}
		},
		"a1": ["b1", "b2", "b3", "b4"],
		"a2": [{
			"b2": {
				"c2": [{
					"d2": {
						"e2": "valueE"
					}
				}]
			}
		}]
	}; 

	cval(testModel, 'a.b.c.d')
	//'valueD'

	cval(testModel, 'a.b.c.d.e.f')
	//''

	cval(testModel, 'a.b.c.d.e.f', 'Error')
	//'Error'

	cval(testModel, 'a2[0].b2.c2[0].d2.e2')
	//valueE

	testModel.cval('a2[0].b2.c2[0].d2.e2');
	//valueE

Advance

	//before
	//if data has error, will throw 'Cannot read property of undefined' error
	if(testModel.a2[0].b2.c2[0].d2.e2){
		//do something
	}

	//ensure version
	if(testModel&&testModel.a2&&testModel.a2[0]&&testModel.a2[0].b2&&testModel.a2[0].b2.c2&&testModel.a2[0].b2.c2){
		//do something
	}


	//now
	var result = cval(testModel, 'a2[0].b2.c2[0].d2.e2', false);
	if(result){
		//do something
	}