export class RegisterComponent {
    public registerForm = this.fb.group({
        name: ['', Validators.required],
        email: ['', [Validators.required, Validators.email]],
        password: ['', [Validators.required, passwordValidator]],
        confirm_password: ['', [Validators.required]],
        agree: [false, Validators.requiredTrue]
    }, {
        validators: confirmValidator()
    });

    constructor(
        private fb: FormBuilder
    ) { }

    get email() {
        return this.registerForm.get('email');
    }

    get password() {
        return this.registerForm.get('password');
    }
}

<form class="form-ico login-form" [formGroup]="registerForm" (ngSubmit)="tapSignUp()">
  <div class="input-group">
        <input type="text" formControlName="name" placeholder="请输入昵称" required="">
        <i class="iconfont icon-user" aria-hidden="true"></i>
    </div>
    <div class="input-group" [class]="{error: email.invalid}">
        <input type="email" formControlName="email" placeholder="请输入邮箱" required="">
        <i class="iconfont icon-at" aria-hidden="true"></i>
    </div>
    <div class="input-group" [class]="{error: password.invalid}">
        <input type="password" formControlName="password" placeholder="请输入密码" required="">
        <i class="iconfont icon-lock" aria-hidden="true"></i>
    </div>
    <div class="input-group" [class]="{error: registerForm.errors && registerForm.errors.confirm}">
        <input type="password" formControlName="confirm_password" placeholder="请确认密码" required="">
        <i class="iconfont icon-check" aria-hidden="true"></i>
    </div>

    <div class="input-group">
        <div class="checkbox">
            <input type="checkbox" formControlName="agree" value="1" id="checkboxInput">
            <label for="checkboxInput"></label>
        </div>
        同意《
        <a href="https://zodream.cn/agreement">本站协议</a>
        》
    </div>

    <button type="submit" class="btn" [disabled]="registerForm.invalid">注册</button>
    <div class="other-box">
        <a routerLink="../">返回登录</a>
    </div>

</form>

export const passwordValidator: ValidatorFn = (control: AbstractControl): ValidationErrors | null => {
  return control.value && control.value.length < 6 ? {
    password_simple: true
  } : null;
};

export const confirmValidator = (key: string = 'password', confirmKey: string = 'confirm_password'): ValidatorFn => {
  return (control: FormGroup): ValidationErrors | null => {
    return control.get(key).value !== control.get(confirmKey).value ? {
      confirm : true
    } : null;
  };
};