Type conversion in javascript

Javascript is a weakly typed language, and variables are type independent, so sometimes we need to do type conversions

Number conversion (number)

Two methods:

ParseFloat, parseInt, parseInt, parseFloat, parseInt, parseFloat, parseInt, parseInt, parseFloat, parseIntCopy the code

number

The reference type is converted to a string (toString) method before the string is converted to a number

String => number: Non-valid number is converted to string Boolean value => Number: 1 or 0 NULL => number: 0; I therefore pay, therefore I am 5. Therefore, I pay, therefore I am 6. Therefore, I pay, therefore I am 6. // 10 Number('10'); // 10 Number(null); // 0 Number(''); // 0 Number(true); // 1 Number(false); // 0 Number([]); / / 0 Number ([1, 2]); // NaN Number('10a'); // NaN Number(undefined); // NaNCopy the code

Parseint () parsefloat ([va], [base]) parseint () parsefloat ([va], [base]) parseint () parsefloat ([va],]) parsefloat ([va],])

If it is not a string, convert it to a string before using this method

Let STR = '12.5px' parseInt(STR)// 12 parseFloat(STR)// 12.5 parseFloat(true)// NaNCopy the code

IsNaN determines the number type:

Return false if the current type is numeric, true otherwise

String conversion (string)

The primitive type, using the toString method () is what did it look like before enclosing quotes around it

Number => String: Enclose quotation marks. NaN => String: 'NaN'. True => String: 'true'. Null => String: 'null' (browser will error (forbid you to use) -- usually can be converted) undefined => string: 'undefined' (browser will error (forbid you to use) -- usually can be converted) Object => string: '[object object]'.Copy the code

Ordinary objects into the results for “[object object]”, because the object. The prototype. The toString method is not converted to a string, but used to detect the data type.

String(123); // "123" String(true); // "true" String(null); // "null" String(undefined); / / "undefined" (error) String ([1, 2, 3]) / / "1, 2, 3" String ({}); // "[object Object]"Copy the code

Boolean type conversion (Boolean)

1.

2: underfined,

3: NaN,

4: null,

5: false,

6:0,

The above six values are false when converted to Booleans, and the others are true

Boolean('') // false
Boolean(undefined) // false
Boolean(null) // false
Boolean(NaN) // false
Boolean(false) // false
Boolean(0) // false 
Boolean({}) // true
Boolean([]) // true
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4. Primitive type conversion

There are two cases of converting a primitive type: to a string type or another primitive type.

If it is already a primitive type, no further conversion is required.

If you convert to a string, the toString() method in the built-in function is called.

If it is any other primitive type, the valueOf() method in the built-in function is called.

If not the original type is returned, the toString() method is continued.

If the original type has not been returned, an error is reported.