ngStyle for dynamic styles in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind a dynamic background color using ngStyle.

Angular

<div [ngStyle]="{'background-color': [1]">Colored Box</div>

Drag options to blanks, or click blank then click option'

Acolor

BbackgroundColor

C'red'

DbgColor

Attempts:

3 left

💡 Hint

Common Mistakes

Using a CSS property name instead of the variable.

Putting the color value directly without quotes or variable.

The variable bgColor holds the dynamic color value used in ngStyle.

2fill in blank

medium

Complete the code to apply multiple dynamic styles using ngStyle.

Angular

<div [ngStyle]="[1]">Styled Text</div>

Drag options to blanks, or click blank then click option'

A{'font-size.px': fontSize, 'color': textColor}

B'font-size.px: fontSize, color: textColor'

C[fontSize, textColor]

DfontSize + textColor

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an object.

Using an array instead of an object.

ngStyle expects an object with style properties as keys and their values. The correct syntax uses curly braces and property-value pairs.

3fill in blank

hard

Fix the error in the ngStyle binding to correctly apply a dynamic width.

Angular

<div [ngStyle]="{'width': [1] + 'px'}">Box</div>

Drag options to blanks, or click blank then click option'

A'widthValue'

BwidthValue

CwidthValue + 'px'

DwidthValuepx

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the variable name inside quotes making it a string literal.

Trying to concatenate inside the string key.

The variable widthValue should be used without quotes inside the expression. The string concatenation happens outside the binding.

4fill in blank

hard

Fill both blanks to set dynamic height and background color using ngStyle.

Angular

<div [ngStyle]="{'height.px': [1], 'background-color': [2]">Box</div>

Drag options to blanks, or click blank then click option'

AboxHeight

BbgColor

C'blue'

DheightValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals instead of variables.

Mixing variable names between height and color.

Use boxHeight for height and bgColor for background color variables from the component.

5fill in blank

hard

Fill all three blanks to create a dynamic style object with font size, color, and margin.

Angular

<p [ngStyle]="{'font-size.px': [1], 'color': [2], 'margin.px': [3]">Text</p>

Drag options to blanks, or click blank then click option'

AfontSize

BtextColor

CmarginSize

Dpadding

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names.

Confusing margin with padding.

Use fontSize, textColor, and marginSize variables to set the respective styles dynamically.

Practice

1. What does the Angular directive ngStyle do?

easy

A. It dynamically applies CSS styles to an element based on an object.

B. It adds classes to an element based on a condition.

C. It binds HTML attributes to an element.

D. It listens to user events like clicks.

Solution

1. Step 1: Understand the purpose of ngStyle

   ngStyle is used to bind an object containing CSS styles to an element dynamically.

2. Step 2: Compare with other directives

   Unlike ngClass which adds/removes classes, ngStyle directly sets inline styles.

3. Final Answer:

   It dynamically applies CSS styles to an element based on an object. -> Option A

4. Quick Check:

   ngStyle = dynamic CSS styles [OK]

Hint: Remember: ngStyle changes styles, ngClass changes classes [OK]

Common Mistakes:

• Confusing ngStyle with ngClass
• Thinking ngStyle listens to events
• Believing ngStyle binds HTML attributes

2. Which of the following is the correct syntax to apply ngStyle in a template?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall the correct binding syntax

   ngStyle expects an object inside square brackets with key-value pairs for styles.

2. Step 2: Check each option

   correctly uses an object with keys and values inside curly braces and quotes for keys with hyphens.

3. Final Answer:

   <div [ngStyle]="{color: 'red', 'font-weight': 'bold'}"></div> -> Option B

4. Quick Check:

   ngStyle = object in square brackets [OK]

Hint: Use square brackets and an object literal for ngStyle [OK]

Common Mistakes:

• Using string instead of object for ngStyle
• Missing square brackets for binding
• Not quoting CSS property names with hyphens

3. Given this component code:

color = 'blue';
isBold = true;

What will be the rendered style of this element?

<div [ngStyle]="{'color': color, 'font-weight': isBold ? 'bold' : 'normal'}">Text</div>

medium

A. Text with default color and normal font weight

B. Text with blue color and normal font weight

C. Text with default color and bold font weight

D. Text with blue color and bold font weight

Solution

1. Step 1: Evaluate the color binding

   The variable color is 'blue', so the style 'color' will be 'blue'.

2. Step 2: Evaluate the font-weight binding

   isBold is true, so the ternary expression returns 'bold'.

3. Final Answer:

   Text with blue color and bold font weight -> Option D

4. Quick Check:

   color=blue and font-weight=bold [OK]

Hint: Check variable values and ternary results carefully [OK]

Common Mistakes:

• Ignoring ternary condition result
• Assuming default styles instead of bound values
• Mixing up true/false in ternary

4. Identify the error in this Angular template snippet:

<div [ngStyle]="{color: color, fontWeight: 'bold'}">Hello</div>

Assuming color is a string variable in the component.

medium

A. The CSS property 'fontWeight' should be quoted as 'font-weight'.

B. The variable 'color' is not defined in the component.

C. ngStyle cannot bind to multiple styles at once.

D. The syntax is correct; no error.

Solution

1. Step 1: Check CSS property naming in ngStyle

   CSS properties with hyphens must be quoted as strings in the object keys, e.g., 'font-weight'.

2. Step 2: Analyze the given code

   The key fontWeight is camelCase and unquoted, which Angular does not convert automatically in ngStyle.

3. Final Answer:

   The CSS property 'fontWeight' should be quoted as 'font-weight'. -> Option A

4. Quick Check:

   CSS keys with hyphens need quotes in ngStyle [OK]

Hint: Quote CSS keys with hyphens in ngStyle object [OK]

Common Mistakes:

• Using camelCase keys without quotes for CSS properties
• Assuming ngStyle accepts unquoted hyphenated keys
• Thinking ngStyle only accepts single style

5. You want to change the background color of a button dynamically based on a component variable isActive. Which ngStyle binding correctly applies a green background when active and gray when inactive?

hard

A. Click me

B. Click me

C. Click me

D. Click me

Solution

1. Step 1: Understand CSS property naming in ngStyle

   CSS properties with hyphens must be quoted as strings, e.g., 'background-color'.

2. Step 2: Check the ternary expression syntax

   Values must be strings, so 'green' and 'gray' need quotes.

3. Step 3: Evaluate each option

   Click me correctly quotes the CSS property and string values. Click me uses camelCase without quotes, which is invalid. Click me quotes the key incorrectly as camelCase. Click me misses quotes around color strings.

4. Final Answer:

   <button [ngStyle]="{'background-color': isActive ? 'green' : 'gray'}">Click me</button> -> Option C

5. Quick Check:

   Quote CSS keys and string values in ngStyle [OK]

Hint: Quote CSS keys with hyphens and string values in ngStyle [OK]

Common Mistakes:

• Using camelCase keys without quotes
• Forgetting quotes around color strings
• Mixing camelCase and hyphenated keys incorrectly