Add Custom Icon in Ionic 2

This is the easiest way I've found, from the forums at https://forum.ionicframework.com/t/anyway-to-custom-the-tabbars-icon-with-my-own-svg-file/46131/36.

In your app.scss file, add the following code:

ion-icon {
    &[class*="appname-"] {
        // Instead of using the font-based icons
        // We're applying SVG masks
        mask-size: contain;
        mask-position: 50% 50%;
        mask-repeat: no-repeat;
        background: currentColor;
        width: 1em;
        height: 1em;
    }
    // custom icons
    &[class*="appname-customicon1"] {
        mask-image: url(../assets/img/customicon1.svg);
    }
    &[class*="appname-customicon2"] {
        mask-image: url(../assets/img/customicon2.svg);
    }
    &[class*="appname-customicon3"] {
        mask-image: url(../assets/img/customicon3.svg);
    }
}

Then in your templates, you can use the following HTML to create the icon:

<ion-icon name="appname-customicon"></ion-icon>

This is far less complicated than using the font-based methods. As long as you're not adding hundreds of icons you should be okay with this method. However each image is sent as a separate request, where as with the font methods all the images are contained in one file, so it would be a little more efficient.

If you want to use custom fonts in ionic 2+ you can do it with following.

Step 01:

• Have/create custom font SVG files using tools such as XD.
• Go to awesome online tool https://icomoon.io to generate font icons out of your SVG files. It's free tool and very good, I am using it for a while.
• Download your custom font file.
• Your file will look like something below.

[class^="icon-"], [class*=" icon-"] {
  font-family: 'icomoon' !important;
  speak: none;
  font-style: normal;
  font-weight: normal;
  font-variant: normal;
  text-transform: none;
  line-height: 1;
}

replace above code with :

[class^="icon-"],
[class*=" icon-"],
[class^="ion-ios-icon"],
[class*="ion-ios-icon"],
[class^="ion-md-icon"],
[class*="ion-md-icon"]{
  @extend .ion;
  font-family: 'icomoon' !important;
  speak: none;
  font-style: normal;
  font-weight: normal;
  font-variant: normal;
  text-transform: none;
  line-height: 1;
}

Step 02:

• We can use SASS @mixing for repetitive work

  @mixin makeIcon($arg, $val) {
  .ion-ios-#{$arg}:before ,
  .ion-ios-#{$arg}-circle:before ,
  .ion-ios-#{$arg}-circle-outline:before ,
  .ion-ios-#{$arg}-outline:before ,
  .ion-md-#{$arg}:before ,
  .ion-md-#{$arg}-circle:before ,
  .ion-md-#{$arg}-circle-outline:before ,
  .ion-md-#{$arg}-outline:before  {
    content: $val;
    font-size: 26px;
  }
}

we can use our sass mixing in our sass file like :

@include makeIcon(icon-new-home, '\e911')

Step 03

Use it like

<ion-tabs class="footer-tabs" [selectedIndex]="mySelectedIndex">
    <ion-tab [root]="tab1Root" tabIcon="home"></ion-tab>
    <ion-tab [root]="tab2Root" tabIcon="icon-new-home"></ion-tab>
 </ion-tabs>

and its even support android ripple effect, which kinda looks cool

[Updated] 30 Nov 2017

@ionic/app-scripts : 3.1.2
Ionic Framework    : ionic-angular 3.9.2

For Ionic 3.1.2

You need to add @import "ionicons"; inside your /src/theme/variables.scss file which will fix below error

"[class^="icon-"]" failed to @extend ".ion". The selector ".ion" was not found. Use "@extend .ion !optional" 
        if the extend should be able to fail.