js常用小技巧

1. string 类型的数字前面+，会转换成 number 类型，且去除数字开头所有的0

  let a1 = '0000.12345'		
  let a2 = '.12345'			
  let a3 = ''				
  let a4 = '000000000000'	
  let a5 = '000000000100'
  
  console.log(+a1)			// 0.12345
  console.log(+a2)			// 0.12345
  console.log(+a3)			// 0
  console.log(+a4)			// 0
  console.log(+a5)			// 100

2. 浮点数，无论 string 还是 numbe r类型，无论正负，直接截断小数部分，转为 number 类型

  let a1 = '0.1111'
  let a2 = '0.9999'
  let a3 = '100.0001'
  let a4 = '100.9999'
  let a5 = 0.1111
  let a6 = 0.9999
  let a7 = 100.0001
  let a8 = 100.9999
  // 0 0 100 100 0 0 100 100
  console.log(~~a1, ~~a2, ~~a3, ~~a4, ~~a5, ~~a6, ~~a7, ~~a8)
  console.log(a1|0, a2|0, a3|0, a4|0 ,a5|0, a6|0, a7|0, a8|0)

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