我见过不同的开发者在javascript的函数后面加分号，也有一些没有。哪种是最佳实践?

function weLikeSemiColons(arg) {
   // bunch of code
};

or

function unnecessary(arg) {
  // bunch of code
}

是否有一种简单的方法来运行单个迁移?我不想迁移到某个版本，我只想运行一个特定的版本。

我如何从java代码动态设置属性layout_weight在android按钮的值?

我正在用React做一个项目，遇到了一个让我难住的问题。

当我运行yarn start时，我得到这个错误:

TypeError [ERR_INVALID_ARG_TYPE]: "path"参数必须是类型 字符串。接收类型未定义

我不知道为什么会这样。

当我试图安装最新版本的compass (https://rubygems.org/gems/compass/versions/1.0.0.alpha.17)时，我得到以下错误。

ERROR:  Error installing compass:
ERROR: Failed to build gem native extension.

 ERROR:  Error installing compass:
  ERROR: Failed to build gem native extension.

    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking for ffi.h... no
checking for ffi.h in /usr/local/include,/usr/include/ffi... yes
checking for ffi_call() in -lffi... yes
checking for ffi_prep_closure()... yes
checking for ffi_raw_call()... no
checking for rb_thread_blocking_region()... yes
checking for rb_thread_call_with_gvl()... yes
checking for rb_thread_call_without_gvl()... yes
checking for ffi_prep_cif_var()... no
creating extconf.h
creating Makefile

make "DESTDIR=" clean

make "DESTDIR="
compiling AbstractMemory.c
compiling ArrayType.c
compiling Buffer.c
compiling Call.c
Call.c:303:5: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
    rbffi_thread_blocking_region(call_blocking_function, data, (void *) -1, NULL);
    ^
./Thread.h:78:39: note: expanded from macro 'rbffi_thread_blocking_region'
# define rbffi_thread_blocking_region rb_thread_call_without_gvl
                                      ^
1 warning generated.
compiling ClosurePool.c
compiling DataConverter.c
DataConverter.c:43:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
compiling DynamicLibrary.c
compiling ffi.c
compiling Function.c
Function.c:479:33: warning: incompatible pointer types passing 'VALUE (void *)' to parameter of type 'void *(*)(void *)' [-Wincompatible-pointer-types]
        rb_thread_call_with_gvl(callback_with_gvl, &cb);
                                ^~~~~~~~~~~~~~~~~
Function.c:102:46: note: passing argument to parameter 'func' here
extern void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
                                             ^
Function.c:563:9: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
        rb_thread_call_without_gvl(async_cb_wait, &w, async_cb_stop, &w);
        ^
Function.c:738:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
3 warnings generated.
compiling FunctionInfo.c
compiling LastError.c
compiling LongDouble.c
compiling MappedType.c
compiling MemoryPointer.c
compiling MethodHandle.c
compiling Platform.c
compiling Pointer.c
compiling Struct.c
compiling StructByReference.c
compiling StructByValue.c
compiling StructLayout.c
compiling Thread.c
compiling Type.c
compiling Types.c
compiling Variadic.c
linking shared-object ffi_c.bundle
clang: error: unknown argument: '-multiply_definedsuppress' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
make: *** [ffi_c.bundle] Error 1

make failed, exit code 2

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/ffi-1.9.3 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-13/2.0.0/ffi-1.9.3/gem_make.out

这是怎么回事?如何正确安装最新的指南针?

如果你曾经使用过JavaScript，你就会知道Internet Explorer没有为Array.prototype.indexOf()[包括Internet Explorer 8]实现ECMAScript函数。这不是一个大问题，因为您可以使用以下代码扩展页面上的功能。

Array.prototype.indexOf = function(obj, start) {
     for (var i = (start || 0), j = this.length; i < j; i++) {
         if (this[i] === obj) { return i; }
     }
     return -1;
}

我应该什么时候实现这个?

我是否应该用下面的检查将它包装在我的所有页面上，检查原型函数是否存在，如果不存在，继续扩展数组原型?

if (!Array.prototype.indexOf) {

    // Implement function here

}

或者做浏览器检查，如果是ie，就实现它?

//Pseudo-code

if (browser == IE Style Browser) {

     // Implement function here

}

正确的方法是什么:

is_array("something") # => false         (or 1)

is_array(["something", "else"]) # => true  (or > 1)

或者获取其中的条目数?

TSQL中for循环的语法是什么?

Ruby <=>(太空船)操作符是什么?运算符是否由其他语言实现?

当我尝试使用一个真正的项目来学习Haskell时，我遇到了下面的定义。我不明白每个论点前面的感叹号是什么意思，我的书似乎也没有提到它。

data MidiMessage = MidiMessage !Int !MidiMessage