Compare avoid empty
If(item !== null){
item.sort();
Item.forEach(function(item){
// execute code
}
}
}
Above judgment item is expected array type, but if the item is numeric or string of words will enter the execution condition if, and only be null comparison is not really safe
Detecting original value
If the desired value is a string, number, Boolean, or undefined, the best option is to use typeof operator, typeof returns a value indicating the type of string
String, typeof returns the string
Digital, typeof Returns number
Boolean value, typeof returns a boolean
undefined，typeof返回undefined
Syntax: ①, typeof variable ②, typeof (variable)
It is undefined undefined variables and the return undefined variables typeof
typeof null is returned object
Null detection is generally not used unless really desired null value, should be compared with the use of congruent null
Detection reference value
Reference value has become the object of several reference types: object, array, date, error
Typeof reference object using object detection return values are
The best type of detection method is to use a reference value instanceof operator
The basic syntax: value instanceof constructor (reference types)
Instanceof detect not only the object constructor, the prototype chain is also detected, by default, every object inherits from the Object, each object value instanceof Object returns a true
And generally do not need to use an array function instanceof
The best method of detection is to use the function to return function typeof
The oldest method of detecting array is identified canard type, if there is sort method by detecting the target variable
More elegant solution: Object.prototype.toString.call (value) === "[object Array]"
Detection property
When detecting a property exists in the object
// bad writing
If(object[propertyName]){
// some code
}
If(object[propertyName] != null){
// some code
}
If(object[propertyName] != undefined){
// some code
}
Actually written over by checking the value of a given attribute name, a value of 0, an empty string, determined that false, null and undefined error occurs.
The best way to determine whether there is an attribute used in operator
var object = {
count:0,
related:null
}
// good writing
if(“count” in object){
// code execution
}
If the detection point of the object's instance attributes are present, use hasOwnProperty () method returns true if this attribute is present instance, if the property is only present in the prototype false if