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I have been reviewing avascript these days. Since this great js was developed by a very powerful person in ten days, there will always be some design flaws. Let us summarize in the study and skip these pitfalls. .
1. Operators == and ===
Pay special attention to the equality operator ==
. When JavaScript is designed, there are two comparison operators:
The first one is ==
comparison, which will automatically convert the data type and then compare. In many cases, very strange results will be obtained. ;
The second type is ===
comparison, which will not automatically convert the data type. If the data types are inconsistent, false
will be returned. If they are consistent, compare again.
Due to this design flaw in JavaScript, Don't use ==
comparisons and always stick to ===
comparisons.
2. NaN
NaN表示Not a Number,当无法计算结果时用NaN表示
NaN
This special Number is not equal to all other values, including itself
NaN === NaN; // false
The only way to judge## The method of #NaN is through the
isNaN() function:
isNaN(NaN); // true3. null and undefined
null represents an "empty" The value is different from
0 and the empty string
''.
0 is a numerical value, and
'' represents a length of 0 String, while
null means "empty".
null. For example, Java also uses
null, Swift uses
nil, and Python uses #. ##None
means. However, in JavaScript, there is also an undefined
similar to null
, which means "undefined". The designers of JavaScript intended to use
to represent an empty value, and undefined
to represent an undefined value. Facts have proved that this is of no use, and the difference between the two is of little significance. In most cases, we should use null
. undefined
It is only useful when judging whether the function parameters are passed 4. Array
An array is a set arranged in order, and each value of the set is called element. JavaScript arrays can contain any data type. For example:
[1, 2, 3.14, 'Hello', null, true];
Initialize the array:
var array1 = new Array()
var array1 = []
var array1 = new Array(10)
5. Object
The object of JavaScript is an unordered set composed of keys and values
var person = { name: 'Bob', age: 20, tags: ['js', 'web', 'mobile'], city: 'Beijing', hasCar: true, zipcode: null };
The keys of JavaScript objects are all string types, and the values can be Any data type. The above
person object defines a total of 6 key-value pairs, each of which is also called an attribute of the object. For example, the name
attribute of person
is 'Bob'
, zipcode
attribute is null
. To get the properties of an object, we use the
method: <pre class="brush:js;toolbar:false;">person.name; // &#39;Bob&#39;
person.zipcode; // null</pre>
Related articles:
Required during the use of JavaScript Things to pay attention to and some basic grammar_Basic knowledge
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