(4) JavaScript Study Notes-data type and value (continued)

1. null1. it is generally regarded as a special value of the object type, that is, the value without an object; 2. when used in a Boolean environment, convert to false, the numeric environment to 0, and the string environment to null. 2. undefined1. use an undeclared variable or a variable without a value, or... syntaxHighlighter. all ();

I. null

1. It is generally regarded as a special value of the object type, that is, the value of "no object;

2. if it is used in a Boolean environment, it is converted to false, the numeric environment is 0, and the string environment is "null ";

Ii. undefined

1. This value is returned when an undeclared variable, a variable without a value assignment, or an object attribute that does not exist;

2. Although it is different from the null value, the = Operator treats the two as equal; www.2cto.com

3. It is used in a Boolean environment. It is converted to false, the numeric environment is NaN, and the string environment is "undefined ";

Iii. Summary of type conversion

 
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