Question

我想为每个循环更改当前对象并且它不起作用，为什么它不起作用，我该怎么做？

var arr = [{num: 1}, {num: 2}];

arr.forEach(function(item) {
  item = {somethingElse: 1}
});

console.log(arr);

Answer 1

它不起作用，因为你所做的只是更新你给出的参数的值（item），它没有与数组的实时连接。一旦您的回调返回，该更改就会消失。

最合适的方法是使用map：

var arr = [{num: 1}, {num: 2}];

arr = arr.map(function(item) {
  return {somethingElse: 1};
});

console.log(arr);

map为每个项目提供函数，并根据您返回的内容构建 new 数组。

如果您在原地更新阵列而不是构建新阵列很重要，那么可以使用forEach，您只需要分配回数组元素即可更新。 forEach回调的第二个参数是您正在访问的索引，因此：

var arr = [{num: 1}, {num: 2}];

arr.forEach(function(item, index) {
  arr[index] = {somethingElse: 1};
});

console.log(arr);

当然，在上述两种情况下，您实际上都在使用item来表示您不在示例代码中的内容...如果您想在{{1}上添加/删除属性}，而不是完全替换对象，Cyril's answer向您展示如何做到这一点。

Answer 2

答案列表的另一种变体

var arr = [{num: 1}, {num: 2}];

arr.forEach(function(item) {
  item.something = 2;//setting the value
  delete item.num;//deleting the num from the object
});

Answer 3

您正在更改回调函数中的本地引用<Page.Resources> <Style x:Key="MyTextBoxStyl" TargetType="TextBox"> <Setter Property="MinWidth" Value="{ThemeResource TextControlThemeMinWidth}"/> <Setter Property="MinHeight" Value="{ThemeResource TextControlThemeMinHeight}"/> <Setter Property="Foreground" Value="{ThemeResource SystemControlForegroundBaseHighBrush}"/> <Setter Property="Background" Value="{ThemeResource SystemControlBackgroundAltHighBrush}"/> <Setter Property="BorderBrush" Value="{ThemeResource SystemControlForegroundChromeDisabledLowBrush}"/> <Setter Property="SelectionHighlightColor" Value="{ThemeResource SystemControlHighlightAccentBrush}"/> <Setter Property="BorderThickness" Value="{ThemeResource TextControlBorderThemeThickness}"/> <Setter Property="FontFamily" Value="{ThemeResource ContentControlThemeFontFamily}"/> <Setter Property="FontSize" Value="{ThemeResource ControlContentThemeFontSize}"/> <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Hidden"/> <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Hidden"/> <Setter Property="ScrollViewer.IsDeferredScrollingEnabled" Value="False"/> <Setter Property="Padding" Value="{ThemeResource TextControlThemePadding}"/> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="TextBox"> <Grid> <Grid.Resources> <Style x:Name="DeleteButtonStyle" TargetType="Button"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="Button"> <Grid x:Name="ButtonLayoutGrid" BorderBrush="{ThemeResource TextBoxButtonBorderThemeBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{ThemeResource TextBoxButtonBackgroundThemeBrush}"> <VisualStateManager.VisualStateGroups> <VisualStateGroup x:Name="CommonStates"> <VisualState x:Name="Normal"/> <VisualState x:Name="PointerOver"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="GlyphElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> <VisualState x:Name="Pressed"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="ButtonLayoutGrid"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="GlyphElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltChromeWhiteBrush}"/> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> <VisualState x:Name="Disabled"> <Storyboard> <DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="ButtonLayoutGrid"/> </Storyboard> </VisualState> </VisualStateGroup> </VisualStateManager.VisualStateGroups> <TextBlock x:Name="GlyphElement" AutomationProperties.AccessibilityView="Raw" Foreground="{ThemeResource SystemControlForegroundChromeBlackMediumBrush}" FontStyle="Normal" FontSize="12" FontFamily="{ThemeResource SymbolThemeFontFamily}" HorizontalAlignment="Center" Text="" VerticalAlignment="Center"/> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style> </Grid.Resources> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="Auto"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition Height="*"/> </Grid.RowDefinitions> <VisualStateManager.VisualStateGroups> <VisualStateGroup x:Name="CommonStates"> <VisualState x:Name="Disabled"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="HeaderContentPresenter"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BackgroundElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledTransparentBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BorderElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundBaseLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledChromeDisabledLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="PlaceholderTextContentPresenter"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledChromeDisabledLowBrush}"/> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> <VisualState x:Name="Normal"/> <VisualState x:Name="PointerOver"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightChromeAltLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource TextControlBackgroundHoverOpacity}"/> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> <VisualState x:Name="Focused"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="PlaceholderTextContentPresenter"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlPageTextChromeBlackMediumLowBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="BackgroundElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundChromeWhiteBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource TextControlBackgroundFocusedOpacity}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="BorderElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAccentBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlForegroundChromeBlackHighBrush}"/> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="RequestedTheme" Storyboard.TargetName="ContentElement"> <DiscreteObjectKeyFrame KeyTime="0" Value="Light"/> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> </VisualStateGroup> <VisualStateGroup x:Name="ButtonStates"> <VisualState x:Name="ButtonVisible"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Visibility" Storyboard.TargetName="DeleteButton"> <DiscreteObjectKeyFrame KeyTime="0"> <DiscreteObjectKeyFrame.Value> <Visibility>Visible</Visibility> </DiscreteObjectKeyFrame.Value> </DiscreteObjectKeyFrame> </ObjectAnimationUsingKeyFrames> </Storyboard> </VisualState> <VisualState x:Name="ButtonCollapsed"/> </VisualStateGroup> </VisualStateManager.VisualStateGroups> <Border x:Name="BackgroundElement" Background="{TemplateBinding Background}" Grid.ColumnSpan="2" Margin="{TemplateBinding BorderThickness}" Opacity="{ThemeResource TextControlBackgroundRestOpacity}" Grid.Row="1" Grid.RowSpan="1"/> <Border x:Name="BorderElement" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="2" Grid.Row="1" Grid.RowSpan="1"/> <ContentPresenter x:Name="HeaderContentPresenter" Grid.ColumnSpan="2" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" Foreground="{ThemeResource SystemControlForegroundBaseHighBrush}" FontWeight="Normal" Margin="0,0,0,8" Grid.Row="0" Visibility="Collapsed" x:DeferLoadStrategy="Lazy"/> <ScrollViewer x:Name="ContentElement" AutomationProperties.AccessibilityView="Raw" HorizontalScrollMode="{TemplateBinding ScrollViewer.HorizontalScrollMode}" HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}" IsTabStop="False" IsHorizontalRailEnabled="{TemplateBinding ScrollViewer.IsHorizontalRailEnabled}" IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}" IsDeferredScrollingEnabled="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}" Margin="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.Row="1" VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}" VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}" ZoomMode="Disabled"/>  <ContentControl x:Name="PlaceholderTextContentPresenter" Grid.ColumnSpan="2" Content="{TemplateBinding PlaceholderText}" Foreground="{ThemeResource SystemControlPageTextBaseMediumBrush}" IsHitTestVisible="False" IsTabStop="False" Margin="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.Row="1" HorizontalAlignment="Center"/> <Button x:Name="DeleteButton" BorderThickness="{TemplateBinding BorderThickness}" Grid.Column="1" FontSize="{TemplateBinding FontSize}" IsTabStop="False" Margin="{ThemeResource HelperButtonThemePadding}" MinWidth="34" Grid.Row="1" Style="{StaticResource DeleteButtonStyle}" Visibility="Collapsed" VerticalAlignment="Stretch"/> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style> </Page.Resources> <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> <TextBox Name="TxtCompanyId" PlaceholderText="FirmaId" Height="40" Margin="5" TextAlignment="Center" Style="{StaticResource MyTextBoxStyl}"/> </Grid>。

要更改数组内容，您需要使用数组索引并为其分配新引用，如下所示

item

Answer 4

您没有处理该对象，因此不会传输更改。

您可以这样做：

Exception in thread "main" java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence near index 1
\mssqlserver1
 ^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.escape(Unknown Source)
    at java.util.regex.Pattern.atom(Unknown Source)
    at java.util.regex.Pattern.sequence(Unknown Source)
    at java.util.regex.Pattern.expr(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.util.regex.Pattern.<init>(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.lang.String.replaceAll(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerConnection.getInstancePort(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriverManager(DriverManagerDataSource.java:153)
    at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriver(DriverManagerDataSource.java:144)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnectionFromDriver(AbstractDriverBasedDataSource.java:155)
    at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnection(AbstractDriverBasedDataSource.java:120)
    at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111)
    at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77)
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:630)
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:909)
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:970)
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:980)
    at com.tutorialspoint.StudentJDBCTemplate.create(StudentJDBCTemplate.java:19)
    at com.tutorialspoint.MainApp.main(MainApp.java:18)

Answer 5

在相关说明中，如果您正在寻找如何更改数组中对象的属性，请记住，您可以仅在forEach循环中对每个对象进行操作更改将保留：

let myArray = [{}];
myArray.forEach((obj) => {obj.foo = "bar";});
console.log(myArray[0].foo); //"bar"

Js为每个循环更改数组内的对象

5 个答案: