About numeric strings

This is the 31st day of my participation in the August Text Challenge.More challenges in August

Number

• NaN is not a significant number, but is of type number
• It’s not equal to any value
• IsNaN ([val]) converts value implicitly to a Number to see if it is not a valid Number. If the value is not a valid Number, return true. If the value is a Number, return false
• To output a value based on alert, the value is implicitly converted to a string.

1. Convert other data types to number

1. Number

• (Number([val]),parseInt(),parseFloat()))

• Implicit conversions are performed based on the Number

  • isNaN([val])
  • Mathematical operation special case + is string concatenation
  • When == is compared, some values need to be converted to numbers for comparison

• To convert a string to a number, all characters in the string must be valid digits

  • Number(“”) => 0 Number(“10”) =>10 Number(“10px”)=> NaN

• Number(true) =>1 Number(false) =>0

• Null => 0 Number(undefined) => NaN

• Symbol cannot be converted to numbers

• To convert an object or function to a number, first convert the object to a string based on toString, and then convert the string to a number

2. parseInt

• The value is converted to a string, and then the first character to the left of the string is searched. All valid digits found are converted to numbers, and the search is stopped until a non-valid digit character is encountered. = > 10 parseInt (” 10.5 px “); = > 10 parseFloat (” 10.5 px “) = > 10.5

3. parseFloat

• ParseFloat simply recognizes one more decimal point than parseInt

Convert other data types to strings

• toString

• String

• Implicit conversion

  • Implicit conversions generally call toString
  • In the + operation, if the + side produces a string, it is not a mathematical operation, but a string concatenation
  • To convert an object to a number, toString() is converted to a string and then to a number.
  • These output methods, based on Alert Confirm Prompt document.write, convert content to string and other types to Boolean

• ! The conversion to a Boolean type is reversed

• !!!!! Convert to a Boolean type

• Boolean ([val])

• In loops or conditional judgments, the result of conditional processing is a Boolean type

• Only “”,0,undefined,null,NaN will become false, the rest will be true

console.log(Number({0:10})); Consoel.log (Number([10])); Console. log(Number([10,20])) toString results in 10,20 with an invalid characterCopy the code

Plus sign in the Js is not necessarily a mathematical operation, as long as the side of a string (or object because digital + object, the theory is put objects into a mathematical operation, but we know that the object into a child, want to call the toString method first, first converted to a string, in converted to strings, met a plus sign and turned into a string concatenation)

parseInt("") > NaN Number("") > 0 isNaN("") > false Number(null) > 0 isNaN(null) >false isNaN(Number(!! Number (parseInt (0.8)))) > false typeof! parseInt(null) + ! IsNaN (null)==== calculates typeof and plusCopy the code

Detection data type