vant/src/step/index.js

import { createNamespace } from '../utils';
import { BORDER } from '../utils/constant';
import { ChildrenMixin } from '../mixins/relation';
import Icon from '../icon';

const [createComponent, bem] = createNamespace('step');

export default createComponent({
  mixins: [ChildrenMixin('vanSteps')],

  computed: {
    status() {
      if (this.index < this.parent.active) {
        return 'finish';
      }
      if (this.index === +this.parent.active) {
        return 'process';
      }
    },
    active() {
      return this.status === 'process';
    },
  },

  methods: {
    genCircle() {
      const { activeIcon, activeColor, inactiveIcon } = this.parent;

      if (this.active) {
        return (
          this.slots('active-icon') || (
            <Icon
              class={bem('icon', 'active')}
              name={activeIcon}
              color={activeColor}
            />
          )
        );
      }

      const inactiveIconSlot = this.slots('inactive-icon');

      if (inactiveIcon || inactiveIconSlot) {
        return (
          inactiveIconSlot || <Icon class={bem('icon')} name={inactiveIcon} />
        );
      }

      return <i class={bem('circle')} />;
    },
  },

  render() {
    const { status, active } = this;
    const { activeColor, direction } = this.parent;

    const titleStyle = active && { color: activeColor };
    const lineStyle = status === 'finish' && { background: activeColor };

    return (
      <div class={[BORDER, bem([direction, { [status]: status }])]}>
        <div class={bem('title', { active })} style={titleStyle}>
          {this.slots()}
        </div>
        <div class={bem('circle-container')}>{this.genCircle()}</div>
        <div class={bem('line')} style={lineStyle} />
      </div>
    );
  },
});