Simple recording for quick review.
// numerical expansion:
console.log (// finite, integer, non-digital judgment
Number.isFinite(10),
Number.isInteger(12),
Number.isInteger(12.1),
Number.isNaN (NaN),
Number.isNaN(10)
)
console.log (// judged positive, negative, 0
Math.sign(2),
Math.sign(0),
Math.sign(-1),
Math.sign('2'), // 1
Math.sign('abc') //NaN
)
console.log (// get the integer part of a decimal
Math.trunc(1.2),
Math.trunc(4.2) // 4
)
// array expansion
console.log(
Array.of(1,2,3,4), // [1, 2, 3, 4]
Array.of(), // []
Array.from ( 'a'), // set into an array
Array.from("http1,http2,http3",item => item.split(',')),
Array.from ([1,2,3], (item) => item * 2) // accepts two parameters, function map array operation
)
console.log(
[1,2, undefined] .fill (7), // [7,7,7] Replace
[ 'A', 'b', 'c', 'd', 'e']. Fill (1,0,3), // 0 from the position 3 to the position of the element, replace 1
[1,2,3,4,5,6,7,8].fill(0,1,2)
)
{ // keys、values、entries
for(let idx in ['a','b','c'].keys()) {
console.log('idx',idx)
}
for(let value in ['a','b','c'].values()) {
console.log('value',value)
}
for(let [index,value] in ['a','b','c'].entries()) {
console.log(` index: ${index}, value: ${value} `)
}
}
{
// find findIndex includes
console.log( [1,2,3,4].find(item => item > 2) )
console.log( [1,2,3,4].findIndex( item => item>2 ) )
console.log( [1,2,3,4].includes(2) )
console.log ([1,2,3, in] .includes (In)) // true
}
{
Alternatively // the index of the element 0, element is used to replace the index between 2 (including 2) the subscript 3
console.log( [1,2,3,'a'].copyWithin(0,2,3)) // [3,2,3,'a']
}