Layouts: How Things Get Positioned

Here's the one idea that, once it lands, makes Ext JS layouts stop fighting you: you do not size things with CSS. The parent's layout sizes its children.

Coming from the web, that's backwards. Normally you slap width: 50% on a div and you're done. In Ext JS, you can set width and height on a component and still watch it render at zero pixels - or vanish entirely - because a container doesn't ask its children how big they want to be. It runs its layout, and the layout decides each child's box. The child is a passenger; the parent's layout drives.

💡 Every layout below is just a different strategy a parent uses to size and place its items. fit means "one child, fill me." hbox means "lay children left to right." border means "children claim edges." Same job, different rule.

Every container has a layout config. Skip it and you get the default - auto - which is exactly where beginners get burned.

The default auto layout (and why it disappoints)

A container with no layout set uses layout: 'auto', which does almost nothing: it stacks children as plain block-level elements, top to bottom, each taking its natural content height with no managed width or height at all.

Ext.create('Ext.panel.Panel', {
    renderTo: Ext.getBody(),
    title: 'Users',
    height: 400,
    // no layout specified -> 'auto'
    items: [
        { xtype: 'grid', /* ...columns, store... */ },
        { xtype: 'form', /* ...fields... */ }
    ]
});

What just happened: the panel is 400px tall, but auto doesn't divide that 400px between the grid and the form - it drops them in as unsized blocks. The grid, having no managed height, often collapses to almost nothing, leaving an empty panel with no obvious cause. Nothing is broken; the parent never told the grid how tall to be. This single misunderstanding is behind most "my Ext JS screen is blank" panic.

The fix is always the same shape: pick a layout that actually sizes the children.

fit - one child, fill the box

fit is the simplest useful layout. The container has exactly one child, and that child is stretched to fill the container completely - full width, full height.

Ext.create('Ext.panel.Panel', {
    renderTo: Ext.getBody(),
    title: 'Users',
    height: 400,
    width: 600,
    layout: 'fit',
    items: [
        { xtype: 'grid', /* columns, store */ }
    ]
});

What just happened: the grid now fills the entire 600×400 panel because fit told it to. This is the canonical pattern for "a panel that wraps a single grid," and you'll see it constantly in legacy code as a window whose only job is to frame one component.

⚠️ fit is built for one child. If you give it multiple items, only the first one shows - the rest are still created but laid out on top / hidden behind it. If you put two things in a fit container and the second vanished, that's not a bug, that's fit doing exactly what it says. You wanted hbox/vbox or card.

hbox / vbox - rows and columns with flex

The box layouts are your workhorses. hbox lays children out in a horizontal row; vbox lays them in a vertical column. The magic ingredient is flex: a number on each child that says how to divide the available space along the main axis proportionally.

Ext.create('Ext.panel.Panel', {
    renderTo: Ext.getBody(),
    title: 'Users',
    height: 400,
    width: 800,
    layout: {
        type: 'hbox',
        align: 'stretch'   // stretch children on the cross-axis (full height)
    },
    items: [
        { xtype: 'grid', flex: 2 /* ...columns, store... */ },
        { xtype: 'form', flex: 1 /* ...fields... */ }
    ]
});

What just happened: hbox puts the grid and form side by side. flex: 2 and flex: 1 split the horizontal space two-to-one, so the grid gets twice the width of the form. align: 'stretch' is the part beginners forget - it stretches both children to the full height of the panel on the cross-axis. Without it, each child is only as tall as its own content, and the grid could collapse again. For vbox, swap the roles: flex divides the height, and align: 'stretch' gives children full width.

Two more knobs worth knowing:

• flex vs fixed size: mix them freely. A child with a fixed width (in hbox) keeps that width, and the flex children share whatever's left over.
• pack and align: pack controls distribution along the main axis ('start', 'center', 'end') - handy for right-aligning toolbar buttons. align controls the cross-axis ('stretch', 'top'/'left', 'middle'/'center', 'bottom').

💡 Mental shortcut: in hbox, flex is about width and align is about height. In vbox, flip them. The "main axis" is the direction the box lays children out; the "cross axis" is the other one.

border - the classic app shell

border is the layout that screams "this is an Ext JS app." Children declare a region - one of 'north', 'south', 'east', 'west', or 'center' - and the layout pins them to the edges of the container. center soaks up whatever space is left.

Here's the users admin shell - a west nav and a center work area:

Ext.create('Ext.container.Viewport', {
    layout: 'border',
    items: [
        {
            xtype: 'panel',
            region: 'west',
            title: 'Navigation',
            width: 220,
            collapsible: true,
            split: true,         // draggable splitter between west and center
            html: 'Users · Roles · Settings'
        },
        {
            xtype: 'panel',
            region: 'center',    // REQUIRED - takes all remaining space
            title: 'Users',
            layout: 'fit',
            items: [ { xtype: 'grid' /* columns, store */ } ]
        }
    ]
});

What just happened: the Viewport fills the whole browser window, and border carves it up. The west nav gets a fixed width: 220, collapsible: true gives it a collapse tool, and split: true adds a draggable splitter so the user can resize it. The center region claims everything that's left and, via its own layout: 'fit', hands all that space to the grid. North/south regions take a fixed height; east/west take a fixed width; center never gets a size from you - it just absorbs the remainder.

⚠️ A border layout must have exactly one center region. This is non-negotiable - leave out center and Ext JS throws an error (older versions) or renders a broken, empty shell. If a border screen is blank, check for a center first. You can have multiple north/south/east/west regions in some setups, but one and only one center, always.

card - show one child at a time

card stacks all its children in the same space but shows only one at a time - think wizards, step-by-step flows, or the body of a tab panel. Switch which child is visible with setActiveItem.

var wizard = Ext.create('Ext.panel.Panel', {
    renderTo: Ext.getBody(),
    width: 500,
    height: 300,
    layout: 'card',
    activeItem: 0,   // start on the first card
    items: [
        { xtype: 'form', title: 'Step 1: Account' },
        { xtype: 'form', title: 'Step 2: Profile' },
        { xtype: 'form', title: 'Step 3: Confirm' }
    ]
});

// later, on a "Next" button:
wizard.getLayout().setActiveItem(1);

What just happened: all three forms exist, but only card 0 is visible at first. setActiveItem(1) swaps the display to the second form - no re-creation, just a visibility switch. You've likely used this without knowing it: Ext.tab.Panel uses a card layout under the hood, and clicking a tab is just setActiveItem for that tab's body.

anchor - sizing relative to the container

anchor sizes children as a percentage (or offset) of the container. You'll meet it in older code:

{
    xtype: 'panel',
    layout: 'anchor',
    items: [
        { xtype: 'textfield', anchor: '100%' },     // full width
        { xtype: 'grid',      anchor: '100% 50%' }  // full width, half height
    ]
}

What just happened: anchor: '100%' makes the textfield span the container's full width; anchor: '100% 50%' gives the grid full width and half the container's height. It works, but it's the older approach - box layouts (hbox/vbox) are usually preferred for new work because flex handles proportional sizing more cleanly. Recognize anchor in legacy screens; reach for box layouts when writing fresh ones.

Layouts nest - and that's the whole trick

No single layout builds a real screen - real screens are layouts inside layouts. The users admin is the textbook case: a border viewport whose center region is itself a vbox holding the grid above the form.

Ext.create('Ext.container.Viewport', {
    layout: 'border',
    items: [
        {
            xtype: 'panel',
            region: 'west',
            title: 'Navigation',
            width: 220,
            split: true,
            collapsible: true
        },
        {
            xtype: 'panel',
            region: 'center',
            title: 'Users',
            layout: { type: 'vbox', align: 'stretch' },  // nested layout
            items: [
                { xtype: 'grid', flex: 1 /* the users list */ },
                { xtype: 'form', height: 180 /* edit selected user */ }
            ]
        }
    ]
});

What just happened: the outer border handles the app shell (nav on the left, work area filling the rest). The center region then runs its own vbox: the grid gets flex: 1 so it grows to fill the leftover vertical space, while the form keeps a fixed height: 180 at the bottom. align: 'stretch' makes both span the full width of the center region. Each container only worries about its own children - nest them and arbitrarily complex screens fall out of simple rules.

⚠️ "Nothing shows up" - the troubleshooting section

💡 If a component is invisible or zero-size, suspect the PARENT'S layout first - not the component. Nine times out of ten the child is fine; the parent never gave it a box.

When something won't render, walk this checklist in order:

1. Is the parent on auto layout? No layout config means auto, which doesn't size children - a grid or panel with no managed height collapses to nothing. Give the parent a real layout (fit, vbox, border...).
2. Is there a border layout with no center? Missing center breaks the whole container. Add exactly one center region.
3. Is a child missing its region? In a border layout, every child needs a region, or it won't lay out.
4. Box layout with no size on the cross-axis? In hbox/vbox, children with no flex and no fixed size on the main axis get zero, and without align: 'stretch' they get zero on the cross-axis too. Add flex, a fixed width/height, or align: 'stretch'.

⚠️ A telltale sign: the component shows up in the DOM and in the component tree (you can find it), but it's 0px tall or 0px wide. That is always a layout problem, never a "the component is broken" problem. Stop inspecting the child's config - go look at how its parent lays things out.

Recap

• The parent's layout sizes its children - not CSS. This is the core mental model; setting width/height on a child often does nothing because the layout overrides it.
• The default auto layout barely sizes anything, which is why unconfigured panels look empty. Pick a real layout.
• fit = one child fills the box; hbox/vbox = rows/columns sized by flex (and align: 'stretch' on the cross-axis); border = edge regions with exactly one required center; card = one child visible at a time via setActiveItem.
• Layouts nest - a border center region can hold a vbox, and that's how real screens (like the users admin) get built.
• When "nothing shows up," check the parent's layout first: auto layout, a missing center, a missing region, or a box child with no size are the usual culprits.

Quick check

Test what sizes a child, and how to read a blank screen:

[
  {
    "q": "You put a grid in a panel, give the grid height: 300, and it still renders at zero height. What's the most likely cause?",
    "choices": ["The grid's store is empty", "The parent panel's layout (probably 'auto') isn't sizing the grid", "You forgot renderTo", "Grids can't have a fixed height"],
    "answer": 1,
    "explain": "In Ext JS the parent's layout sizes children. An 'auto' layout doesn't manage height, so the child collapses no matter what height you set on it."
  },
  {
    "q": "Which statement about the border layout is correct?",
    "choices": ["You must have exactly one 'center' region", "The 'center' region needs a fixed width", "You can have at most one 'west' region and no 'center'", "Regions are optional and default to 'north'"],
    "answer": 0,
    "explain": "A border layout requires exactly one center region; it absorbs the space left after the edge regions take their fixed sizes."
  },
  {
    "q": "In an hbox layout, what does flex: 2 on one child and flex: 1 on another do?",
    "choices": ["Stretches both to full height", "Splits the available WIDTH two-to-one between them", "Splits the available HEIGHT two-to-one", "Shows only the first child"],
    "answer": 1,
    "explain": "In hbox, flex divides the available space along the main (horizontal) axis, so flex 2 vs 1 gives the first child twice the width. Cross-axis height is controlled by align: 'stretch'."
  }
]