【Better Code】repeat

《JavaScript 框架设计》

版本1:

function repeat(target, n) {
return (new Array(n + 1)).join(target)
}

版本2:

function repeat(target, n) {
return Array.prototype.join.call({length: n + 1}, target)
}

版本3:(缓存)

var repeat = (function() {
var join = Array.prototype.join,
obj = {}
return function(target, n) {
obj.length = n + 1
return join.call(obj, target)
}
})();

版本4:(算法)

function repeat(target, n) {
var s = target,
total = []
while (n > 0) {
if (n % 2 == 1) total[total.length] = s
if (n == 1) break
s += s
n = n >> 1
} return total.join('')
}

版本5:

function repeat(target, n) {
var s = target,
c = s.length * n
do {
s += s
} while (n = n >> 1)
s = s.substring(0, c)
return s
}

版本6:

function repeat(target, n) {
var s = target
total = ''
while (n > 0) {
if (n % 2 == 1) total += s
if (n == 1) break
s += s
n = n >> 1
}
return total
}

版本7:(递归)

function repeat(target, n) {
if (n == 1) {
return target
}
var s = repeat(target, Math.floor(n / 2))
s += s
if (n % 2) {
s += target
}
return s
}
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