What are the cast rules?

The forced type conversion rules are: 1. Convert characters to numerical values. [parseInt()] converts from left to right once. If it can be converted, it will be converted. If it cannot be converted, it will stop. [Math.round()] is strictly converted and cannot be converted. Any non-numeric characters are allowed; 2. Convert numerical values ​​to characters, [toString()] directly converts.

The forced type conversion rule is:

Character to value

parseInt();Convert from left to right once. If it can be turned, it will be turned, and if it cannot be turned, it will stop; if it is the first place, it cannot be turned, and it will be NaN directly; the decimal point will not be recognized.

parseFloat();Equivalent to parseInt, and can recognize decimal points

Math.round();Strict conversion, no non-standard conversion is allowed Numeric characters, otherwise NaN; take the nearest integer

Number();Strict conversion, no non-numeric characters are allowed, otherwise NaN; direct conversion

var str = "123";

var str = "123abc";

var str = "123abc456";

var str = "a123";

var str = "adasd";

var str = "123.45";

var n = parseInt(str);

console.log(str);

console.log(typeof str);

console.log(n);

console.log(typeof n);

var str = "a567.892";

var n = parseFloat(str);

console.log(str);

console.log(typeof str);

console.log(n);

console.log(typeof n);

var str = "-456.789";

var n = Math.round (str);

console.log(str);

console.log(typeof str);

console.log(n);

console.log(typeof n);

var str = "-456.789a";

var n = Number(str);

console.log(str);

console.log(typeof str);

console.log(n);

console.log(typeof n);

Numeric value to character

toString();Direct conversion is equivalent to adding quotation marks to the value to be converted

Keep n as a decimal

toFixed();While adding quotation marks, round to n decimal places. If it is not enough, add zeros

var n = 10.3543;

var s = n.toString( );

console.log(n);

console.log(typeof n);

console.log(s);

console. log(typeof s);

var n = 10;

var s = n.toFixed(2);

console.log(n);

console.log(typeof n);

console.log(s);

console.log(typeof s);

console.log(123.567000000)

Numeric value to character

var n = 123;

var s = n "";

console.log(s)

Character to value

var s = "123";

var n = s - 0;

console.log (n)

Other rotation values

true is 1, false is 0

console.log(1 true); //2

console.log(1 false); //1

console.log(1 undefined); //NaN

console.log(1 NaN); //NaN

console.log(1 null); //1

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