Question

现在我正在使用此函数来确定数字是否为整数：

function isInteger(input){
    return (input%1==0);
}

有更有效的方法吗？我知道这里有一个内置的javascript函数，但它在某些IE版本中不起作用。

Answer 1

根据jsPerf，~~（repeated bitwise NOT）和<< 0（向左移0位）在我的浏览器中更快：

function isInteger(input) {
  return (~~input === input);
}

function isInteger2(input) {
  return (input << 0 === input);
}

警告：JavaScript按位运算符将其操作数强制转换为signed 32-bit integers，因此此方法仅对Math.pow(2, 31) -1（2147483647）之前的数字安全。如果您不能保证，请使用其他方法。

在其他方法中，n % 1 === 0和Math.floor(value) === value的速度慢了40-50％，Number.isInteger落后了。

然而，它们都“非常快”。除非您必须检查批次数字，否则这些方法都不会成为您应用程序的瓶颈。

Answer 2

bool parse(const char* line, char* abs_path, char* query)
{
    // TODO
    // Get the lenght of line
    int l = strlen(line);

    // Store the place in the string 
    int a = 0;

    // Stores number of total spaces
    int spaces = 0;

    // Iterate in line
    for (int i = 0; i < l; i++)
    {// Look for spaces
        if (isspace(line[i]) == 0)
        {
            spaces++;
        }
    }
    // If there are more than the 2 required spaces
    if (spaces > 2)
    {
        error(400);
        printf("400 Bad Request\n");
        return false;
    }
    // If request - target doen't begin with "/"

    // Look for the fist space
    for (int i = 0; i < l; i++)
    {// Look for space
        if (isspace(line[i]) == 0)
        {
            a = i + 1;
            break;
        }
    }

    if (line[a] != '/')
    {
        error(501);
        printf("501 not implemented\n");
        return false;
    }


    {
        error(405);
        printf("405 Method Not Allowed\n");
        return false;
    }

    // If request-target contains "
    // Will store position of second space
    int b = 0;
    // Look for the second space
    for (int i = a; i < l; i++)
    {
        if (isspace(line[i]) == 0)
        {
            b = i;
            break;
        }
    }
    // Find if there is a " in request-target
    for (int i = a; i < b; i++)
    {
        if ( line[i] == '"')
        {   
            error(400);
            printf("400 Bad Request\n");
            return false;
        }
    }

    // If HTTP version isn't HTTP/1.1
    char http[7] = "";
    for (int i = b + 1; i < (b + 1) + 7/*Chars 
    from the second space till the end of HTTP/1.1*/;i++)
    {
        http[i] = line[i];
    }

    if (strcmp(http, "HTTP/1.1") != 0)
    {
        error(505);
        printf("505 HTTP Version Not Supported\n");
        return false;
    }

    // Store absolute-path at the address in abs_path and the query string at query

    // Separate the query
    // String to store the query
    char query2[8190 + 1] = "";

    // Store the position in line where the query string starts
    int c = 0;
    // Counter for query array
    int q = 0;
    for (int i = b - 1/*before the space after the query*/; i > a/*after the first space*/;i--)
    {
        if (line[i] == '=')
        {
            c = i - 1;
            break;
        }

    }
    // Pass the string to query2
    for (int i = c; i < (b - 1); i++)
    {
        query2[q] = line[i];
        q++;
    }
    // If there is no query, make query2 empty
    if (query2[0] != 'q')
    {
        strcpy(query2, "");
    }

    // Allocate query2 and query at the heap
    query = malloc(sizeof(query2));

    // Copy query2 to query
    strcpy(query, query2);

    // Separate absolute path
    // Declare char array to store absolute path
    char abs1[8190 + 1] = "";

    // Make space at the heap

    abs_path = malloc(sizeof(abs1));

    for (int i = a /*where the / after the first space starts*/; i < (c - 1);
    i++)
    {
        abs1[i] = line[i];
    }

    // Copy abs to abs_path
    strcpy(abs_path, abs1);

    return true;


}

来源：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger#Polyfill

Answer 3

TextInfo.ToTitleCase()

是否有更高效或通常更好的方法来确定数字是否是一个整数？

3 个答案: