返回任意次数的字符串的最佳或最简洁的方法是什么?
以下是我目前为止拍得最好的照片:
function repeat(s, n){
var a = [];
while(a.length < n){
a.push(s);
}
return a.join('');
}
当前回答
各种方法的测试:
var repeatMethods = {
control: function (n,s) {
/* all of these lines are common to all methods */
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return '';
},
divideAndConquer: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
with(Math) { return arguments.callee(floor(n/2), s)+arguments.callee(ceil(n/2), s); }
},
linearRecurse: function (n,s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return s+arguments.callee(--n, s);
},
newArray: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return (new Array(isNaN(n) ? 1 : ++n)).join(s);
},
fillAndJoin: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
var ret = [];
for (var i=0; i<n; i++)
ret.push(s);
return ret.join('');
},
concat: function (n,s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
var ret = '';
for (var i=0; i<n; i++)
ret+=s;
return ret;
},
artistoex: function (n,s) {
var result = '';
while (n>0) {
if (n&1) result+=s;
n>>=1, s+=s;
};
return result;
}
};
function testNum(len, dev) {
with(Math) { return round(len+1+dev*(random()-0.5)); }
}
function testString(len, dev) {
return (new Array(testNum(len, dev))).join(' ');
}
var testTime = 1000,
tests = {
biggie: { str: { len: 25, dev: 12 }, rep: {len: 200, dev: 50 } },
smalls: { str: { len: 5, dev: 5}, rep: { len: 5, dev: 5 } }
};
var testCount = 0;
var winnar = null;
var inflight = 0;
for (var methodName in repeatMethods) {
var method = repeatMethods[methodName];
for (var testName in tests) {
testCount++;
var test = tests[testName];
var testId = methodName+':'+testName;
var result = {
id: testId,
testParams: test
}
result.count=0;
(function (result) {
inflight++;
setTimeout(function () {
result.start = +new Date();
while ((new Date() - result.start) < testTime) {
method(testNum(test.rep.len, test.rep.dev), testString(test.str.len, test.str.dev));
result.count++;
}
result.end = +new Date();
result.rate = 1000*result.count/(result.end-result.start)
console.log(result);
if (winnar === null || winnar.rate < result.rate) winnar = result;
inflight--;
if (inflight==0) {
console.log('The winner: ');
console.log(winnar);
}
}, (100+testTime)*testCount);
}(result));
}
}
其他回答
String.prototype.repeat现在是ES6标准。
'abc'.repeat(3); //abcabcabc
function repeat(s, n) { var r=""; for (var a=0;a<n;a++) r+=s; return r;}
各种方法的测试:
var repeatMethods = {
control: function (n,s) {
/* all of these lines are common to all methods */
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return '';
},
divideAndConquer: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
with(Math) { return arguments.callee(floor(n/2), s)+arguments.callee(ceil(n/2), s); }
},
linearRecurse: function (n,s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return s+arguments.callee(--n, s);
},
newArray: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
return (new Array(isNaN(n) ? 1 : ++n)).join(s);
},
fillAndJoin: function (n, s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
var ret = [];
for (var i=0; i<n; i++)
ret.push(s);
return ret.join('');
},
concat: function (n,s) {
if (n==0) return '';
if (n==1 || isNaN(n)) return s;
var ret = '';
for (var i=0; i<n; i++)
ret+=s;
return ret;
},
artistoex: function (n,s) {
var result = '';
while (n>0) {
if (n&1) result+=s;
n>>=1, s+=s;
};
return result;
}
};
function testNum(len, dev) {
with(Math) { return round(len+1+dev*(random()-0.5)); }
}
function testString(len, dev) {
return (new Array(testNum(len, dev))).join(' ');
}
var testTime = 1000,
tests = {
biggie: { str: { len: 25, dev: 12 }, rep: {len: 200, dev: 50 } },
smalls: { str: { len: 5, dev: 5}, rep: { len: 5, dev: 5 } }
};
var testCount = 0;
var winnar = null;
var inflight = 0;
for (var methodName in repeatMethods) {
var method = repeatMethods[methodName];
for (var testName in tests) {
testCount++;
var test = tests[testName];
var testId = methodName+':'+testName;
var result = {
id: testId,
testParams: test
}
result.count=0;
(function (result) {
inflight++;
setTimeout(function () {
result.start = +new Date();
while ((new Date() - result.start) < testTime) {
method(testNum(test.rep.len, test.rep.dev), testString(test.str.len, test.str.dev));
result.count++;
}
result.end = +new Date();
result.rate = 1000*result.count/(result.end-result.start)
console.log(result);
if (winnar === null || winnar.rate < result.rate) winnar = result;
inflight--;
if (inflight==0) {
console.log('The winner: ');
console.log(winnar);
}
}, (100+testTime)*testCount);
}(result));
}
}
简单的方法:
String.prototype.repeat = function(num) {
num = parseInt(num);
if (num < 0) return '';
return new Array(num + 1).join(this);
}
小提琴:http://jsfiddle.net/3Y9v2/
function repeat(s, n){
return ((new Array(n+1)).join(s));
}
alert(repeat('R', 10));
